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Item 1A. Risk Factors.

Certain risk factors can significantly impact our business, liquidity, capital resources, results of operations, financial condition, and debt ratings. These risk factors might affect, alter, or change actions we might take executing our long-term capital strategy. Examples include, without limitation, contributing capital to any or all of the Insurance Subsidiaries, issuing additional debt and/or equity securities, repurchasing our existing debt and/or equity securities, or increasing or decreasing stockholders’ dividends. We operate in a continually changing business environment and new risk factors emerge from time to time. Consequently, we can neither predict such new risk factors nor assess the potential future impact, if any, they might have on our business.

Risks Related to COVID-19

Governmental actions to contain or delay the spread of the COVID-19 pandemic since early March 2020 have disrupted ordinary business commerce and impacted financial markets. These governmental actions, for which we cannot predict the extent, duration, and possible alteration based on future COVID-19-related developments, could materially and adversely affect our results of operations, financial position, and liquidity.

These actions generally have:

•Negatively impacted the global and United States domestic economies, with some sectors such as travel and leisure, retail, energy, and real estate more significantly affected than others;

•Increased unemployment;

•Increased international, federal, state, and local government budget deficits, which has led to adverse rating actions against certain governmental units and increased the general risk of government debt default that could impact the value of related fixed income securities;

•Induced significant volatility in financial markets;

•Decreased valuations in markets for equity, fixed income, and alternative investments in certain sectors;

•Impacted individual income and business revenue, and increased the number of individuals and businesses experiencing financial distress with the potential for insolvency;

•Decreased premium collections, late payment fees, and reinstatement fees;

•Generated state and federal legislative or executive branch proposals to (i) require insurance policies to retroactively cover COVID-19-related losses expressly excluded under the terms of some property insurance policies, and (ii) presume that COVID-19 is a work-related illness for certain employees under workers compensation policies;

•Generated state insurance department bulletins or orders requesting or mandating premium credits and rebates on certain insurance policies that may exceed actual COVID-19-related frequency experience decreases;

•Disrupted commerce, supply chains, and travel to varying degrees;

•Increased expense management focus by individuals and all-sized businesses;

•Increased the demand for and/or limited the availability of certain types of medical resources; and

•Increased e-commerce, video, phone, and other methods of remote trade and business transaction.

The economic impacts of the COVID-19-related governmental actions may impact our revenue, loss and loss expense, liquidity, or regulatory capital and surplus, and operations, particularly as these relate, without limitation, to the following:

Impact on Our Insurance Operations

•Because our general liability and workers compensation policies provide for premium audit to assure pricing for actual risk exposure, we must estimate return premium that we may owe policyholders for revenues and payrolls lowered by the extent and duration of the COVID-19-related governmental directives and related economic contraction. Such return premiums could be significant and will impact our underwriting results. Our results include the impact of a $75 million return audit and mid-term endorsement premium accrual recorded in the first quarter of 2020, which reflects our estimate of reduced exposures on the in-force workers compensation and general liability portfolio as of March 31, 2020. As of December 31, 2020, we had a remaining accrual of $24.8 million.

•In the second quarter of 2020, we offered a credit equal to 15% of insureds’ premiums for our standard lines commercial automobile and personal automobile lines of insurance for April and May totaling $19.7 million. This two-month premium credit was based on a limited amount of claims reporting data reflecting the impact of the COVID-19-related governmental directives on miles driven, which has reduced claims frequencies. Due to the sudden and dynamic nature of these impacts, we did not rely upon traditional actuarial analysis to support these credits. We will not know the actual impact of the COVID-19-related governmental actions until some point in the future. Should the various governmental directives be extended or reinstated due to increased infection rates, we may give further premium credit to our customers to the extent supported by further analysis. Based on the continued COVID-19-related economic impact, state insurance commissioners may take other regulatory actions requiring additional premium credits in commercial and personal automobile and other lines, and we face the risk that we may be required to return more premium than is warranted by our filed rating plans and actual loss experience.

•All of our commercial property and businessowners' policies require direct physical loss of or damage to property by a covered cause of loss to trigger a business interruption claim. Whether COVID-19-related contamination, the existence of a pandemic, and/or the resulting government shutdown orders cause physical loss of or damage to property continues to be the subject of much debate and litigation. We cannot predict the outcome of that litigation. Our practice is to include in, or attach to, all standard lines commercial property and businessowners' policies an

exclusion that states that all loss or property damage caused by or resulting from any virus, bacterium, or other microorganism that induces or is capable of inducing physical distress, illness, or disease is not a covered cause of loss. We offer some limited coverages that could apply in COVID-19-related claims and circumstances, primarily tied to clean-up and food-contamination that are subject to sub-limits. Approximately 95% of our commercial property and businessowners' policies include the very specific and regulatory approved virus exclusion.

•We purchase a significant amount of reinsurance, including a property catastrophe reinsurance program and property and casualty excess of loss reinsurance treaties. In response to the COVID-19 pandemic and recent increased catastrophic loss activity, the reinsurance industry is seeking to tighten contractual terms and conditions, reduce reinsurance capacity, and increase its pricing for reinsurance protection. Tightened terms and conditions include introducing new coverage exclusions, such as excluding losses related to communicable diseases, particularly for business interruption losses in property treaties and, to a lesser extent, in casualty treaties. To the extent we are exposed to losses on our primary policies from risks, such as communicable disease, these losses will most likely be excluded from coverage under our new reinsurance treaties, and we now face increased underwriting risk. This increased underwriting risk could increase our net loss and loss expenses and increase the volatility in our underwriting results. We experienced risk-adjusted reinsurance price increases at our January 1, 2021 renewals that were at rates higher than we are likely able to generate on the underlying insurance policies we sell.

•In response to the COVID-19 pandemic, there currently are various public policy debates and legislative and regulatory proposals at both the federal and state levels:

◦Certain states have proposed legislation that would impose liability (including retroactively) for COVID-19-related business interruption losses on policies that do not provide such coverage terms. We cannot predict the outcome of such proposals. We believe that if any of these proposals were enacted, they could impair future commercial activity and would likely be determined unconstitutional after being challenged through litigation. Nonetheless, if such proposals were enacted and upheld as constitutional, they could have a material impact on our profitability, liquidity, and overall financial condition and results of operations.

◦We are aware of four future pandemic insurance proposals being discussed in Washington, D.C., only one of which has been introduced as proposed legislation. Three of the proposals provide for insurer participation and put insurer capital at risk to various degrees. If any of the proposals involving insurer at risk capital were enacted, it could have a material impact on our profitability, liquidity, and overall financial condition and results of operations.

◦Certain state insurance departments have indicated that they currently (i) will not approve the filing of rate increases or decreases related – or unrelated – to COVID-19, and (ii) are suspending, limiting, or restricting the approval or attachment of new virus-related exclusions. To the extent any of these regulatory actions do not permit us to modify our rating plans, they could have a material impact on our profitability, liquidity, and overall financial condition and results of operations.

•Limited medical resources availability could result in medical inflation and complicate, delay and/or extend medical treatment that could impact exposure on workers compensation, general liability, and personal and commercial automobile claims.

•Economic inflation could increase our loss and loss expense reserves, particularly associated with our longer tail lines of business.

•We may have increased workers compensation loss and loss expenses if policyholders' employees in high-risk roles of essential businesses contracted COVID-19 in the workplace. We may experience higher frequency of workers compensation claims, particularly as state legislative or executive order proposals are enacted that create presumptions that the contraction of COVID-19 by an essential business employee who interacted with the public is work-related. We also may see an extension of workers compensation benefits if employees do not have jobs to which they can return.

•We may experience an increase in liability claims against our policyholders related to business practices as remote-office work-from-home employees return to their pre-COVD-19 office and business locations. This may be exacerbated by an active plaintiffs’ bar seeking to generate COVID-19-related claim activity.

•Loss frequency and severity could increase related to our auto and property coverages due to, among other things,

disruptions in supply chains and changes in business practices and individual behaviors resulting from the shelter-in-place and social distancing measures, such as arson and fraud.

•Due to the COVID-19-related governmental orders, we may experience delayed reporting of losses, settlement negotiations, and trial of disputed claims that may disrupt our normal claims resolution processes and trends.

•Service levels could deteriorate if significant numbers of our (i) employees were to be simultaneously infected by COVID-19, whether working remotely or in one of our offices, and/or (ii) remote employees or key business partners are unable to work effectively while sheltering-in-place. Examples of potential work impacts include local internet disruption that prevents access to our virtual private network or similar unavoidable events. Because our employees are working remotely, it also is possible that we will be subject to increased cybersecurity attacks from bad actors.

Impact on our Investment Operations

•The COVID-19 pandemic and the related governmental orders may result in further significant equity and debt market volatility that could impact our net investment income due to the following:

◦Financial market volatility is reflected in our alternative investment portfolio performance;

◦A change in spreads on fixed income securities may create mark-to-market investment valuation losses and volatility in unrealized capital gains, which will impact GAAP equity;

◦Losses on securities that we intend to sell may increase, as we give our third-party investment managers flexibility to take advantage of the spread widening in fixed income securities, particularly in asset classes more significantly impacted by COVID-19-related governmental directives and to which the Federal Reserve Board is providing liquidity and structural support;

◦Economic inflation related to COVID-19 issues could be higher or lower than our expectations and impact our investment returns; and

◦A potential increase in credit risk associated with municipal bonds for which repayment is supported by dedicated revenue streams that may be impacted by COVID-19.

Impact on our Capital Position, Liquidity and Financial Leverage

•Out of an abundance of caution, we significantly increased our short-term debt during the first quarter of 2020 to enhance our liquidity and provide us with additional financial flexibility due to the market volatility and economic uncertainty from the COVID-19 pandemic. These short-term borrowings totaled $302 million, and we invested the proceeds in high-quality money market funds and fixed income securities. In addition to the $302 million of short-term borrowings, our GAAP equity decreased from $2.2 billion at December 31, 2019 to $2.1 billion at March 31, 2020, driven by a reduction in net unrealized gains in our investment portfolio. The combination of the additional borrowings and lower GAAP equity resulted in an increase in our debt to total capitalization ratio from 20.1% at December 31, 2019 to 28.9% at March 31, 2020, above our longer term target of 25%.

•We subsequently repaid these short-term borrowings by December 31, 2020.The reduction in the short-term borrowings, as well as an increase in our GAAP equity to $2.7 billion at December 31, 2020, inclusive of our issuance on December 2, 2020, of $200.0 million of 4.60% non-cumulative preferred stock ("Preferred Stock"), has decreased our debt to total capitalization ratio to 16.7% at December 31, 2020.

Despite the improvement in our capital position and a reduction in our debt to total capitalization since the first quarter of 2020, the ongoing COVID-19 pandemic, in future periods, could cause a reduction in our GAAP income or equity, decrease our liquidity, and result in an increase in our debt to total capitalization.This could impact our financial strength ratings and impair our business.

Risks Related to our Insurance Operations

We are subject to losses from catastrophic events.

Losses from natural and human-made catastrophes including, without limitation, hurricanes, tornadoes, windstorms, earthquakes, hail, severe winter weather, derechos, floods, and fires, some related to climate change - and terrorism, including cyber-attacks, civil unrest, and explosions, can negatively impact our financial results. The frequency and severity of these catastrophes are inherently unpredictable. In recent years, the global insurance industry has seen an escalation in the frequency and severity of losses from catastrophes.

The United Nation’s Intergovernmental Panel on Climate Change (“IPCC”) is an international body responsible for assessing climate change science. In 2018, the IPCC reported in its "Special Report on Global Warming of 1.5°C" that human activities are estimated to have caused approximately 1.8°F of global warming above pre-industrial levels and that, if the trend continues at the current rate, it will reach 2.7°F above pre-industrial levels between 2030 and 2052. Climate change models project robust differences in global regional climate characteristics between 1.8°F and 3.6°F. These differences, whether attributable to human activities or natural, include increases in (i) mean temperature in most land and ocean regions, (ii) hot extremes in most inhabited regions, (iii) heavy precipitation in several regions, and (iv) the probability of drought and precipitation deficits in some regions. These differences and increases can impact weather patterns and the frequency and severity of catastrophes including hurricanes, severe convective storms, and wildfires. The IPCC's 2019 "Special Report on Climate Change and Land" reinforced these findings.

Our insurance operations primarily write risks in the Eastern, Midwestern, and Southwestern regions of the U.S. Our most significant catastrophe exposures are (i) hurricanes impacting the Eastern U.S., (ii) terrorism events, (iii) severe convective storms, including hailstorms and tornadoes, and (iv) winter storms. Single storms could adversely impact our financial results, but it is also possible that we could experience more than one severe catastrophic event in any given calendar year. We track our severe weather and catastrophe losses using definitions and information we obtain from ISO’s Property Claim Services unit, an internationally recognized expert on U.S. storm losses.

Certain factors can impact our estimates of ultimate costs for catastrophes, including:

i.Inability to access portions of the impacted areas following a catastrophic event;

ii.Scarcity of necessary labor and materials that delay repairs and increase our loss costs;

iii.Regulatory uncertainties, including new or expanded interpretations of coverage;

iv.Residual market assessment-related increases in our catastrophe losses;

v.Potential fraud and inflated repair costs, partly driven by (a) demand surge post-event, and (b) opportunistic service providers;

vi.Higher loss adjustment expenses due to shortages of claims adjusters available to appraise damage;

vii.Late claims reporting;

viii.Escalation of business interruption costs due to infrastructure disruption; and

ix.Whether the U.S. Secretary of Treasury certifies a terrorist event as an act of terrorism under TRIPRA.

An increase in catastrophe losses likely will reduce our net income and stockholders’ equity and could have a material adverse effect on our liquidity, financial strength, and debt ratings. The closer a catastrophe occurs to the end of a reporting period, the more likely it is we have limited information to estimate loss and loss expense reserves, adding greater uncertainty to our estimates. More detailed claims information available after the end of a reporting period may result in reserve changes in subsequent periods.

Our loss and loss expense reserves may not be adequate to cover actual losses and expenses.

We maintain reserves for our estimated liability for loss and loss expense associated with reported and unreported insurance claims. We base our loss and loss expense reserve estimates on known facts and circumstances, including our expectations of ultimate settlement and claim administration expenses, trends in claims severity and frequency, medical inflation trends, predictions of future events, and other subjective factors relating to our in-force insurance policies. There is no method for precisely estimating the ultimate liability for the settlement of claims.

Reserve estimates may be impacted by a variety of broad economic, political, social, and legal developments or trends, such as inflation, judicial tort decisions, and various state legislative initiatives. Because we cannot predict the timing and impact of these economic, political, social, and legal developments or trends, and estimating loss and loss expense reserves is inherently uncertain, we cannot be sure the reserves we establish are adequate or will be so in the future.

We review our reserve position quarterly and adjust the reserve position accordingly. An increase in reserves (i) reduces net income and stockholders’ equity, and (ii) could have a material adverse effect on our liquidity, financial strength, and debt

ratings. As we underwrite new business and renew existing business, we estimate future loss cost trends in pricing our products to generate an adequate risk-adjusted return. If our estimate of future loss cost trends proves to be understated, our pricing of future new and renewal business may be inadequate to meet estimated loss costs trends, understating our future loss and loss expense reserves.

The COVID-19 pandemic is an example of how loss and loss expense reserves might be affected by economic, political, social, or legal developments or trends. Two additional examples are:

•If economic inflation, including medical inflation, is higher than our assumptions, our loss and loss expense reserves associated with our longer tail lines of business may prove to be insufficient. In particular, our workers compensation line of business is susceptible to this risk, given its extended payment pattern and the current low medical inflationary environment compared to long-term medical inflation rates, which have historically been higher.

•Several states have expanded or are exploring expanding the statute of limitations for civil actions alleging sexual abuse. By retroactively permitting claims for previously time-barred acts, these “reviver” laws may result in insurance claims that could significantly increase loss costs and require re-evaluation of previously-established reserves or the creation of new reserves. Since reviver statutes have been enacted, we have received notices of claims or potential claims for acts alleged to have occurred as far back as the 1950s. Without prior experience, we cannot estimate how many "reviver" claims notices we may receive. Most notices we have received are sent on behalf of claimants by attorneys unsure of what insurer or policy (if any) may have covered the alleged assailant or supervising entity and may not implicate insurance policies issued by us or a predecessor. For notices we have determined implicate an insured under a policy issued by us or a predecessor, we (i) have investigated or are investigating facts, (ii) have evaluated policy terms, and (iii) believe we have appropriate coverage defenses and reinsurance protections that have been considered in establishing our reserves. As coverage positions may be challenged through litigation or otherwise, we face litigation risks further discussed below in the Risk Factor entitled, “Incidental to our insurance operations, we are engaged in ordinary routine legal proceedings that, because litigation outcomes are inherently unpredictable, could impact our reputation and/or have a material adverse effect on our consolidated results of operations or cash flows in particular quarterly or annual periods.”

For further discussion on our loss and loss expense reserves, please see the “Critical Accounting Policies and Estimates” section of Item 7. “Management’s Discussion and Analysis of Financial Condition and Results of Operations.” and Note 2. "Summary of Significant Accounting Policies" in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K.

Our ability to reduce our risk exposure depends on the availability and cost of reinsurance.

We transfer a significant portion of our underwriting risk exposure - specifically a portion of our loss and loss expense - to reinsurance companies in exchange for a specified portion of premiums. Most of our reinsurance contracts have annual terms. The availability, amount, and cost of reinsurance depend on market conditions, including retrocessional reinsurance market capacity. This may fluctuate significantly and not necessarily correlate to the loss experience of our specific book of business. In general, we can consider catastrophe reinsurance expense in our filed rates and rating plans. Any other disproportionate increase in our reinsurance expense that we cannot include in our filed rates and rating plans will reduce our earnings. If we do not obtain expected reinsurance amounts or terms, our reinsurance expenses could increase, we may assume increased risk for individual or aggregate losses, and our ability to write future business could be adversely affected.

Catastrophes impact many property and casualty insurance lines, but commercial property and homeowners coverages historically have accounted for most of our catastrophe-related claims. To limit our exposure to catastrophe losses, we purchase catastrophe reinsurance. It is possible that our reinsurance coverage could be inadequate, particularly if:

•We do not purchase sufficient amounts of reinsurance because of defects or inaccuracies in the various modeling software programs we use to analyze our Insurance Subsidiaries' risk;

•A major catastrophe loss exceeds the purchased reinsurance limit or is within the limits, but exceeds the financial capacity of one or more of our reinsurers;

•The frequency of catastrophe losses increases and our Insurance Subsidiaries' insured losses exceed the aggregate limits of the catastrophe reinsurance treaty or our Insurance Subsidiaries experience an aggregation of losses that fall below our per occurrence reinsurance retention; or

•Our reinsurance counterparties (a) are unable to access their reinsurance markets, or retrocessions, (b) suffer significant financial losses, (c) are sold, (d) cease writing reinsurance business, or (e) are unable or unwilling to satisfy their contractual obligations to us.

Typically, our reinsurance contracts align with our primary insurance policies. For example, if our primary insurance policies provide coverage for a loss, then our reinsurance contracts typically provide coverage as well (subject to any specific exclusions the reinsurance contracts may contain).

In response to the COVID-19 pandemic and recent increased catastrophic loss activity, the reinsurance industry has sought to tighten contractual terms and conditions, reduce reinsurance capacity, and increase pricing. Tightened terms and conditions include introducing new coverage exclusions, such as excluding losses related to cyber risk and communicable diseases, particularly for business interruption losses in property treaties and, to a lesser extent, in casualty treaties. To the extent we are exposed to losses on our primary policies from risks, such as cyber and communicable disease, that are now principally excluded from coverage under our reinsurance treaties, we face increased underwriting risk. The increased underwriting risk could increase our net loss and loss expenses and increase the volatility in our underwriting results. Decreased reinsurance capacity also would increase our underwriting risk if we cannot fully place our existing reinsurance treaties upon renewal. We experienced risk-adjusted reinsurance price increases at our January 1, 2021 renewals that were at rates higher than we are likely to generate on the underlying insurance policies we sell. This will negatively impact our underwriting profitability in 2021.

Even with the benefits of reinsurance, our exposure to catastrophe risks could have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings.

We may be subject to potentially significant losses from acts of terrorism.

We are required to participate in TRIPRA, which was extended to December 31, 2027, for our Standard Commercial Lines and E&S Lines business. TRIPRA rescinded all previously-approved coverage exclusions for terrorism and requires private insurers and the U.S. government to share the risk of loss on future acts of terrorism certified by the U.S. Secretary of the Treasury. Under TRIPRA, each participating insurer is responsible for paying a significant deductible of specified losses before federal assistance is available. Our deductible of $369 million is based on a percentage of our prior year’s applicable Standard Commercial Lines and E&S Lines premiums. For losses above the deductible in 2021, the federal government will pay 80% of losses, and the insurer retains 20%. Although TRIPRA’s provisions provide some mitigation to our loss exposure to a large-scale terrorist attack, our deductible could have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings. If the U.S. Secretary of Treasury does not certify certain future terrorist events, as happened with the 2013 Boston Marathon bombing and the 2015 San Bernardino shootings, we could be required to pay terrorism-related covered losses without TRIPRA's risk-sharing benefits. We also could be required to pay terrorism-related losses for customers who declined terrorism coverage.

Under TRIPRA, terrorism coverage is mandatory for all primary workers compensation policies. TRIPRA also applies to cyber liability insurance policies reported under a Terrorism Risk Insurance Program-eligible line of insurance. Insureds with non-workers compensation commercial policies have the option to accept or decline our terrorism coverage or negotiate with us for other terms. In 2020, 86% of our Standard Commercial Lines non-workers compensation policyholders purchased terrorism coverage that included nuclear, biological, chemical, and radioactive ("NBCR") events.

Many states in which we write commercial property insurance mandate that we cover fire following an act of terrorism - regardless of whether the insured opted to purchase terrorism coverage. We also sometimes elect to provide terrorism coverage for lines of business not included in TRIPRA, such as Commercial Automobile. TRIPRA has never covered personal lines of business. Our homeowner policies in Standard Personal Lines exclude nuclear losses, but they do not exclude biological or chemical losses. Our current reinsurance programs generally provide coverage for conventional acts of foreign and domestic terrorism, but afford no coverage for NBCR events.

We are exposed to credit risk.

We face credit risk in several areas of our insurance operations, including from:

•Our reinsurers, which are obligated to make payments to us under our reinsurance agreements. Reinsurance credit risk can fluctuate over time, increasing during periods of high industry catastrophe losses. Reinsurers generally manage their large loss exposure through their own reinsurance programs, or retrocessions, about which we do not always have the full details. If our reinsurers have difficulty collecting on their retrocession programs or in reinstating retrocession coverage after a large loss, we may not receive timely or full payment of our reinsurance claims. This means that we have direct and indirect counterparty credit risk to our reinsurers and the reinsurance industry, which is global but relatively small.

•Certain life insurance companies obligated to our policyholders or claimants under annuities we purchased as part of structured claims settlements, if they fail to fulfill their annuity contract obligations.

•Some of our independent distribution partners, who collect premiums from our policyholders for us.

•Some policyholders directly obligated to us for premium and/or deductible payments, the timing of which may be impacted by mandated payment moratoriums.

Our exposure to credit risk could have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings.

We depend on distribution partners.

We market and sell our insurance products through independent, non-employee distribution partners. Insurance law and regulation makes us responsible for the business practices and customer interactions of our distribution partners. Independent distribution partners have, and we expect will continue to have, a significant role in overall insurance industry premium production. While our customers find advantages in using independent distribution partners, our reliance on independent distribution partners presents risks and challenges, including:

•Competition in our distribution channel, as independent distribution partners have access to products from multiple carriers and markets, and we must market our products and services to our distribution partners before they sell them to our mutual customers.

•Challenges in developing brand recognition that require us to closely coordinate with our distribution partners, as some customers cannot differentiate their insurance agent from their insurance carrier.

•Our market share growth is tied to the growth in market share controlled by our distribution partners. Independent retail insurance agencies control 85% of standard commercial lines business and 36% of standard personal lines business in the U.S. Consequently, expansion of our Standard Personal Lines market opportunity could be more limited than our Standard Commercial Lines business. More competitors have focused on lower-cost "direct-to-the-customer" distribution models that emphasize digital ease and technological efficiencies to address the discrepancy in agency control of Standard Personal Lines business. Continued advancements in "direct-to-the-customer" distribution models may impact the overall market share controlled by our independent distribution partners and make it more difficult for us to grow, or require us to establish relationships with more distribution partners.

•Aggregation and consolidation of our independent distribution partners and their market share, as some publicly-traded and private equity-backed independent distribution partners have deployed consolidation strategies to acquire other independent distribution partners and increase their market share ("Aggregators") over the last decade. If more of our independent distribution partners become Aggregators, or are acquired by Aggregators, Aggregator demands and influence on our business could increase. For example, Aggregators could develop and implement strategies to consolidate their business with fewer insurers and demand higher base and supplemental commissions. Aggregators accounted for approximately 33% of our DPW at December 31, 2020, up from 20% three years ago. Currently, no one distribution partner is responsible for 10% or more of our combined insurance operations' premium.

Our financial condition and results of operations are impacted by our independent distribution partners' success in marketing and selling our products and services.

National and global economic conditions could adversely and materially affect our business, results of operations, financial condition, and growth.

Unfavorable economic developments, such as those that occurred during the COVID-19 pandemic, could adversely affect our earnings if our policyholders need less insurance coverage, cancel existing insurance policies, modify coverage, or choose not to renew with us. An economic downturn also could lead to increased credit and premium receivable risk, failure of reinsurance counterparties and other financial institutions, limitations on our ability to issue new debt, reduced liquidity, and declines in our investments' fair value and financial strength ratings. These potential events and other economic factors could adversely and materially affect our business, results of operations, financial condition, and growth. During 2020, 29% of DPW in our Standard Commercial Lines business was based on payroll/sales of our underlying policyholders. An economic downturn in which our policyholders experience declines in revenue or employee count could adversely affect our audit and endorsement premium in our Standard Commercial Lines.

A downgrade or a potential downgrade in our financial strength or credit ratings could result in a loss of business and could have a material adverse effect on our financial condition and results of operations.

A significant financial strength rating downgrade, particularly from AM Best, would affect our ability to write new or renewal business. Most policyholders are required by various third-party agreements to use a carrier with a specified minimum AM Best or S&P rating. Downgrades in our credit ratings also could make it more expensive for us to access capital markets. We cannot predict the possible rating actions NRSROs might take that could adversely affect our business or our potential actions in response. Any significant downgrade in our financial strength and credit ratings could have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings. For additional information on our current financial strength and credit ratings, refer to "Overview" in Item 1. "Business." of this Form 10-K.

Markets for insurance products and services are highly competitive and subject to rapid technological change, and we may be unable to compete effectively.

We offer our insurance products and services in a highly competitive market characterized by aggressive price competition and downward pressure on gross margins, introduction of new products and services, evolving industry standards, continual improvement in product pricing based on performance characteristics, rapid competitor adoption of technological advancements, and consumer and business price sensitivity. Our ability to compete successfully depends heavily on our ability to ensure timely and consistent introduction of innovative new products and services through digital platforms.

We face substantial competition from a wide range of property and casualty insurance companies for customers, distribution partners, and employees. Competitors include public, private, and mutual insurance companies. Many competitors are larger and may have lower operating costs, lower cost of capital, or the ability to absorb greater risk while maintaining their financial strength ratings. Other competitors, such as mutual or reciprocal companies, are owned by or operated cooperatively for insureds and, unlike us, do not have shareholders who evaluate return on equity performance. Consequently, some competitors may be able to price their products more competitively.

The Internet has emerged as a significant competitive marketplace for existing and new competitors. Established insurance competitors, such as The Progressive Corporation, are beginning to explore broader digital offerings on the Internet, while new competitors, such as Lemonade, Root, Metromile, and Next, continue to emerge. Because the Internet makes it easier and less expensive to bundle products and services, it also is possible that companies conducting business on the Internet, in the future, could enter the insurance business or form strategic alliances with insurers. Changes in competitors and competition, particularly on the Internet, could cause changes in the supply or demand for insurance and adversely affect our business.

The increasing importance of the Internet, technology, and digital strategy in our industry also highlights our need to attract and retain employees in difficult-to-fill data science, advanced analytics, and IT roles – and the potential negative impact if we fail in so doing.

We have less loss experience data than our larger competitors.

Insurers rely on access to reliable data about their policyholders and loss experience to build complex analytics and predictive models that assess risk profitability, reserve adequacy, adverse claim development potential, recovery opportunities, fraudulent activities, and customer buying habits. Because we use and rely on the aggregated industry loss data assembled by rating bureaus under the anti-trust exemptions of the McCarran-Ferguson Act, we likely would be at a competitive disadvantage to larger insurers if Congress repealed the McCarran-Ferguson Act.

We expect the use of data science and analytics to continue to increase and become more complex and accurate, particularly with larger sets of relevant data. Some larger competitors have significantly more data about the performance of their underwritten risks. In comparison, we may not have sufficient volumes of loss experience data to analyze and project our future costs as accurately or granularly. To supplement our data, we use industry loss experience from ISO, AAIS, NCCI, and other publicly available sources. While relevant, industry data may not correlate specifically to the performance of risks we have underwritten and may not be as predictive as data on a larger book of our own business.

We are subject to various modeling risks that could have a material adverse impact on our business results.

We rely on complex financial and other statistical models, developed internally and by third parties, that predict (i) underwriting results on individual risks and our overall portfolio, (ii) claims fraud and other claims impacts, such as escalation, (iii) impacts from catastrophes, (iv) enterprise risk management capital scenarios, and (v) investment portfolio changes. We rely on these financial and other statistical models to analyze historical loss costs and pricing, trends in claims severity and frequency, the occurrence of catastrophe losses, determining reinsurance attachment and exhaustion points, investment performance, portfolio risk, and our economic capital position. Flaws in these financial and other statistical models, or in the embedded assumptions, could lead to increased losses. We believe that statistical models are extremely valuable in monitoring and controlling risk, but they are not a substitute for senior management's experience or judgment.

Risks Related to Our Investments Segment

Our investments are exposed to credit risk, interest rate fluctuation, and changes in value.

We depend on income from our investment portfolio for a significant portion of our revenue and earnings. Our investments can be negatively affected by liquidity, credit deterioration, financial results, market and economic conditions, political risk, including changes in U.S. Presidential administration, sovereign risk, interest rate fluctuations, or other factors. Our investment portfolio's value is subject to credit risk from the issuers, and/or guarantors and insurers, of the securities we hold, and other counterparties in certain transactions. Defaults on any of our investments by any issuer, guarantor, insurer, or other counterparty could reduce our net investment income and net realized investment gains - or result in investment losses. We are subject to the risk that the issuers or guarantors of fixed income securities we own may default on principal and interest payment obligations.

Additionally, we are exposed to interest rate risk, primarily related to the market price, and cash flow variability associated with changes in interest rates. Consequently, the value and liquidity of our cash, cash equivalents, and marketable and non-marketable securities may fluctuate substantially. Future fluctuations in the value of our cash, cash equivalents, and marketable and non-marketable securities could result in significant losses and have a material adverse impact on our financial condition and operating results.

Significant future declines in investment value also could require further losses recorded on securities we intend to sell and credit losses. For more information regarding market interest rate, credit, and equity price risk, see Item 7A. “Quantitative and Qualitative Disclosures About Market Risk.” of this Form 10-K.

We have securities tied to LIBOR, which may be eliminated by the end of 2021.

As of December 31, 2020, approximately 13% of our fixed income securities portfolio was comprised of floating rate securities tied to the U.S. dollar-denominated London Interbank Offered Rate ("LIBOR"), expected to be eliminated by the end of 2021. The global banking industry has used LIBOR as a primary metric to calculate interest rates for numerous types of debt obligations, including personal and commercial loans, interest rate swaps, and other derivative products. In anticipation of LIBOR's elimination, the U.S. Federal Reserve established the Alternative Reference Rates Committee ("ARRC") to select a replacement index for U.S. Dollar LIBOR. The ARRC, comprised of a broad group of private-market participants, including banks, asset managers, insurers, and industry regulators, identified the Secured Overnight Financing Rate ("SOFR") as the recommended benchmark rate to replace LIBOR. SOFR is based on overnight repurchase agreement transactions backed by Treasury securities. The ARRC announced a paced transition plan for this new rate, including specific steps and timelines designed to encourage the adoption of SOFR. We continue to monitor the potential impact, if any, the elimination of LIBOR and the transition to SOFR will have on our floating rate investments' performance.

We are subject to the types of risks inherent in investing in private limited partnerships.

Our other investments include investments in private limited partnerships that invest in various strategies, such as private equity, private credit, and real assets. The primary assets and liabilities underlying the investments in these limited partnerships generally do not have quoted prices in active markets for the same or similar assets, so their valuation is subject to a higher level of subjectivity and unobservable inputs than substantially all of our other investments. Because these limited partnership investments are recorded under the equity method of accounting, any valuation decreases could negatively impact our results of operations. We currently expect to increase our allocation to these investments, which may produce additional variability in our net investment income.

The determination of the amount of credit losses taken on our investments is highly subjective and could materially impact our results of operations or our financial position.

The determination of the amount of credit losses taken on our investments is based on our periodic evaluation and assessment of our investments and known and inherent risks associated with the various asset classes. Such evaluations and assessments are revised as conditions change and new information becomes available. Management updates its evaluations regularly and reflects changes in credit losses at the time of evaluation. There can be no assurance that management has accurately assessed the level of credit losses taken as reflected in our Financial Statements. For further information about our evaluation and considerations for determining whether a security has a credit loss, please refer to “Critical Accounting Policies and Estimates” in Item 7. “Management’s Discussion and Analysis of Financial Condition and Results of Operations.” of this Form 10-K.

Risks Related to Evolving Laws, Regulation, and Public Policy Debates

We are subject to complex and changing laws, regulations, and public policy debates that expose us to regulatory scrutiny, potential liabilities, increased costs, reputational harm, and other adverse effects on our business.

Our operations are subject to complex and changing state and federal laws, regulations, and public policy debates on subjects, including, without limitation, the following:

•Pricing and underwriting practices;

•Claims practices;

•Loss and loss adjustment expense reserves;

•Exiting geographic markets and/or canceling or non-renewing policies;

•Environmental, social, and governance ("ESG") issues, including ESG investment mandates;

•Assessments for guaranty funds and second-injury funds, and other mandatory assigned risks and reinsurance;

•The types, quality, and concentration of investments we make;

•Minimum capital requirements for the Insurance Subsidiaries;

•Dividends from our Insurance Subsidiaries to the Parent;

•Privacy and data security;

•Tax;

•Antitrust;

•Consumer protection;

•Advertising;

•Sales;

•Billing and e-commerce;

•Intellectual property ownership and infringement;

•Digital platforms;

•Internet, telecommunications, and mobile communications;

•Media and digital content;

•Availability of third-party software applications and services;

•Labor and employment;

•Anti-money laundering; and

•Workplace environmental, health, and safety issues.

We continue to monitor and engage in industry and public policy discussions about related legislative and regulatory changes. Changes to laws and regulations can adversely affect our business by increasing our costs, limiting our ability to offer a product or service to customers, requiring changes to our business practices, or otherwise making our products and services less attractive to customers.

If Congress enacted a law directly regulating insurance, particularly insurer solvency oversight, and state regulators remained responsible for rate approval, we could be subject to a conflicting and inconsistent regulatory framework that could impact our profitability and capital adequacy.

While we underwrite risks only in the U.S., international regulatory developments, particularly in the European Union (“EU”) related to global capital standards, may influence U.S. regulators as they develop or revise domestic regulatory standards. The International Association of Insurance Supervisors proposed Basic Capital Standards for Global Systemically Important Insurers and a uniform capital framework for internationally active insurers in 2014. Two years later, the EU enacted Solvency II, which established new insurer capital adequacy and risk management requirements intended to reduce the possibility of consumer loss or market disruption by European insurers. Despite these international regulatory changes and continued public policy discussion, RBC remains the NAIC capital adequacy standard. The FIO, in coordination with the Federal Reserve, state regulators, and other regulatory bodies, has been exploring group capital standards. In the fourth quarter of 2020, the NAIC's Group Capital Calculation Working Group adopted the basic structure of its new Group Capital Calculation, along with the model law changes necessary to incorporate it as a requirement for U.S. insurance groups in state law.

We have implemented policies and procedures designed to ensure compliance with applicable laws and regulations. However, we can provide no assurance that our employees, contractors, or independent distribution partners will not violate such laws and regulations or our policies and procedures. To some degree, we have multiple regulators whose authority may overlap and may have different interpretations and/or regulations related to the same legal issues. This creates the risk that one regulator's position or interpretation may conflict with another regulator on the same issue. The cost of complying with various, potentially conflicting laws and regulations, and changes in those laws and regulations, could have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings.

Insurers are subject to intense regulatory, political, and media scrutiny. We are subject to government market conduct review and investigations, legal actions, and penalties. There can be no assurance that our business will not be materially adversely affected by the outcomes of such examinations, investigations, or media scrutiny in the future. If we are found to have violated laws and regulations, it could materially adversely affect our reputation, financial condition, and operating results.

Our business is subject to a variety of state, federal, and other laws, rules, policies, and other obligations regarding data protection.

We are subject to federal, state, and international laws relating to the collection, use, retention, security, and transfer of personally identifiable information (“PII”). Federal laws include the Gramm-Leach-Bliley Act, the Fair Credit Reporting Act, the Drivers Privacy Protection Act, the Health Insurance Portability and Accountability Act, and Federal Trade Commission policies. Several states, like New York, Nevada, and California, have passed laws in this area, and other jurisdictions are considering imposing additional restrictions or creating new rights concerning PII. These laws continue to develop and may be inconsistent from jurisdiction to jurisdiction. Complying with emerging and changing requirements may cause us to incur substantial costs or require us to change our business practices. Noncompliance could result in significant reputational harm, penalties, and legal liability.

In the same year that it adopted Solvency II, the EU adopted the General Data Protection Regulation ("GDPR"). Effective since 2018 after a two-year implementation period, GDPR regulates data protection and privacy in the EU and transfers of personal data outside the EU. GDPR’s main tenet is to give individuals primary control over their personal data. While GDPR has no direct impact on U.S. companies like us without an EU presence, it and any future EU data privacy actions may influence U.S. regulators over time.

We make statements about our use and disclosure of PII through our privacy policy, information provided on our website, and other public statements. If we fail to comply with these public statements or federal, state, and international privacy-related and data protection laws and regulations, we could be subject to litigation or governmental actions. Such proceedings could impact our reputation and result in penalties, including ongoing audit requirements and significant legal liability.

We are engaged in ordinary routine legal proceedings incidental to our insurance operations that, because litigation outcomes are inherently unpredictable, could impact our reputation and/or have a material adverse effect on our consolidated results of operations or cash flows in particular quarterly or annual periods.

We are engaged in ordinary routine legal proceedings incidental to our insurance operations that include:

•Defense of or indemnity for third-party suits brought against our insureds;

•Defense of actions brought against us by our insureds who disagree with our coverage decisions, some of which allege bad faith claims handling and seek extra-contractual damages, punitive damages, or other penalties;

•Actions we file, primarily for declaratory judgment, seeking confirmation that we have made appropriate coverage decisions under our insurance contracts;

•Actions brought against us or competitors alleging improper business practices and sometimes seeking class status. Such actions historically have included issues and allegations, without limitation, related to (i) unfairly discriminatory underwriting practices, including the impact of credit score usage, (ii) managed care practices, such as provider reimbursement, and (iii) automobile claims practices; and

•Actions we file against third parties and other insurers for subrogation and recovery of other amounts we paid on behalf of our insureds.

From time-to-time, legal proceedings in which we are involved may receive media attention based on their perceived newsworthiness and/or relationship to a variety of broad economic, political, social, and legal developments or trends. Such media stories could negatively impact our reputation.

We expect that any potential ultimate liability for ordinary routine legal proceedings incidental to our insurance business will not be material to our consolidated financial condition after considering estimated loss provisions. Litigation outcomes, however, are inherently unpredictable even with meritorious defenses. The time a case is in litigation also is unpredictable, as state court dockets are increasingly overcrowded. Generally, the longer a case is in litigation the more expensive it can become. Because the amounts sought in certain of these actions are large or indeterminate, any adverse outcomes could have a material adverse effect on our consolidated results of operations or cash flows in particular quarterly or annual periods.

Risks Related to Our Corporate Structure and Governance

We are a holding company, and our ability to declare dividends to our shareholders, pay indebtedness, and enter into affiliate transactions may be limited because our Insurance Subsidiaries are regulated.

Restrictions on our Insurance Subsidiaries' ability to pay dividends, make loans or advances to the Parent, or enter into transactions with affiliates may materially affect our ability to pay dividends on our preferred stock and common stock, or repay our indebtedness.

In 2021, the Insurance Subsidiaries can provide the Parent with $241 million in ordinary annual dividends under applicable state regulation. Still, their ability to pay dividends or make loans or advances is subject to their domiciliary state insurance regulator's approval or review. For additional details regarding dividend restrictions, see Note 22. “Statutory Financial Information, Capital Requirements, and Restrictions on Dividends and Transfers of Funds” in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K.

The Parent’s ability to pay dividends to its common stockholders is also impacted by covenants in its credit agreement (the “Line of Credit”) among the Parent, the lenders named therein (the “Lenders”), and the Bank of Montreal, Chicago Branch, as Administrative Agent, that obligate it to, among other things, maintain a minimum consolidated net worth and a maximum ratio of debt to capitalization. Under the terms of our Preferred Stock, the Parent's ability to declare or pay dividends on, or purchase, redeem or otherwise acquire, shares of its common stock or any shares of the Parent that rank junior to, or on parity with, the Preferred Stock will be subject to certain restrictions if the Parent does not declare and pay (or set aside) dividends on the Preferred Stock for the last preceding dividend period. For additional details about the Line of Credit’s financial covenants, see Note 11. “Indebtedness” in Item 8. "Financial Statements and Supplementary Data" of this Form 10-K. For additional details about conditions related to our Preferred Stock, see Note 17. "Preferred Stock" in Item 8. "Financial Statements and Supplementary Data" of this Form 10-K.

Because we are a New Jersey corporation and an insurance holding company, we may be less attractive to potential acquirers and the value of our common stock could be adversely affected.

We are a New Jersey company, and provisions of the New Jersey Shareholders’ Protection Act and our Amended and Restated Certificate of Incorporation may discourage, delay, or prevent us from being acquired. A supermajority of our shareholders must approve (i) certain business combinations with interested shareholders, or (ii) any amendment to the related provisions of our Amended and Restated Certificate of Incorporation unless certain conditions are met. These conditions may relate to, among other things, the interested stockholder’s acquisition of stock, the approval of the business combination by disinterested members of our Board and disinterested stockholders, and the price and payment of the consideration proposed in the business combination. In addition to considering the effects of any action on our shareholders (including any offer or proposal to acquire the Parent), our Board may consider: (i) the long-term, as well as the short-term, interests of the Parent and our shareholders, including the possibility that these interests may best be served by the continued independence of the Parent; (ii) the effects of the action on the Parent's employees, suppliers, creditors, and customers; and (iii) the effects of the action on the community in which the Parent operates.

These provisions of our Amended and Restated Certificate of Incorporation and New Jersey law could deprive our common shareholders of an opportunity to receive a premium over the prevailing market price in the event of a hostile takeover and may adversely affect the value of our common stock.

Because we own insurance subsidiaries, any party seeking to acquire 10% or more of our common stock must seek prior approval from the subsidiaries' domiciliary insurance regulators and file extensive information about their business operations and finances.

Risks Related to Our General Operations

We, our distribution partners, and our vendors are subject to attempted cyber-attacks, other cybersecurity risks, and system availability risk.

Our business heavily relies on IT and application systems that may be accessed from, or are connected to, the Internet. Consequently, a malicious cyber-attack could affect us. Our systems also contain proprietary and confidential information, including PII, about our operations, employees, agents, and customers and their employees and property. A malicious cyber-attack on (i) our systems, (ii) our distribution partners or their key operating systems, and (iii) any other of our third-party partners or vendors and their key operating systems may interrupt our ability to operate, damage our reputation and result in monetary damages that are difficult to quantify, and have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings.

We have implemented systems and processes, through encryption and authentication technologies, intended to mitigate or secure our IT systems and prevent unauthorized access to, or loss of, sensitive data. Our security measures may not be sufficient for all eventualities, as cyber-attacks are continuing to evolve daily. We may be vulnerable to hacking, employee error, malfeasance, system error, faulty password management, or other irregularities. Any disruption or breach of our systems or data security could damage our reputation, result in monetary damages that are difficult to quantify, and have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings. To mitigate this risk, we have and expect to continue to (i) conduct employee education programs and tabletop exercises and (ii) develop and invest in a variety of controls to prevent, detect, and appropriately react to cyber-attacks, including frequently testing our systems' security and access controls. We have insurance coverage for certain cybersecurity risks, including privacy breach incidents, which provides coverage up to $30 million above a $1 million deductible. Such coverage may be insufficient to indemnify all losses or types of claims that may arise.

In addition to cyber-attack risk, we face system availability risk. Our business relies heavily on various IT and application systems that may be impacted by an unplanned loss of availability unrelated to malicious cyber-attacks. A failure in one or more systems, including those at facilities where we or our vendors operate systems, may interrupt our ability to operate and negatively impact our results of operations.

Our long-term strategy to deploy operational leverage is dependent on the success of our risk management strategies, and their failure could have a material adverse effect on our financial condition or results of operations.

As an insurer, we assume risk from our policyholders. Our long-term strategy includes the use of above-average operational leverage, which can be measured as the ratio of NPW to our equity or policyholders' surplus. We balance and mitigate our operational leverage risk with several risk management strategies within our insurance operations to achieve a balance of growth and profit, including purchasing significant amounts of reinsurance, a disciplined approach to reserving, and a conservative investment philosophy. These strategies have inherent limitations. We cannot be certain that an event or series of unanticipated events will not occur and result in losses greater than we expect and have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings.

Item 1B. Unresolved Staff Comments.

None.

Item 2. Properties.

Our headquarters occupy a 315,000 square foot building located on a 56-acre site zoned for office and professional use in Branchville, New Jersey, and is also the home to our solar facility. The site is owned by a subsidiary that also owns abutting property in Frankford, New Jersey. We lease all our other facilities from unrelated parties. The principal office locations of our insurance operations are listed in the “Geographic Markets” section of Item 1. “Business.” of this Form 10-K. Our Investments operations are principally located in leased space in Farmington, Connecticut. Our facilities provide adequate space for our present needs and, if additional space is needed, should be available on reasonable terms.

Item 3. Legal Proceedings.

Incidental to our insurance operations, we are engaged in ordinary routine legal proceedings that, because litigation outcomes are inherently unpredictable, could have a material adverse effect on our consolidated results of operations or cash flows in particular quarterly or annual periods. For additional information regarding our legal risks, refer to Item 1A. “Risk Factors.” and Note 21. "Litigation" included in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K. As of December 31, 2020, we have no material pending legal proceedings that could have a material adverse effect on our consolidated financial condition, results of operations, or cash flows.

PART II

Item 5. Market For Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities.

(a) Market Information

Our common stock is traded on the NASDAQ Global Select Market under the symbol “SIGI.”

(b) Holders

We had 3,051 common stockholders of record as of February 4, 2021, according to the records maintained by our transfer agent.

Dividends on shares of our common stock are declared and paid at the discretion of the Board of Directors (the "Board") based on our results of operations, financial condition, capital requirements, contractual restrictions, and other relevant factors. We currently expect to continue to pay quarterly cash dividends on shares of our common stock in the future.

On October 28, 2020, the Board approved a 9% increase in our common stock dividend to $0.25 per share. In addition, on January 28, 2021, the Board declared a $0.25 per share quarterly cash dividend on common stock that is payable March 1, 2021, to stockholders of record as of February 12, 2021.

(d) Securities Authorized for Issuance under Equity Compensation Plans

The following table provides information about our common stock authorized for issuance under equity compensation plans as of December 31, 2020:

(a) (b) (c)

Equity compensation plans approved by security holders — $ — 4,876,140

1Includes 257,088 shares available for issuance under our Employee Stock Purchase Plan (2009); 1,659,233 shares available for issuance under the Stock Purchase Plan for Independent Insurance Agencies; and 2,959,819 shares for issuance under the Selective Insurance Group, Inc. 2014 Omnibus Stock Plan ("Stock Plan"). Future grants under the Stock Plan can be made, among other things, as stock options, restricted stock units, or restricted stock.

(e) Performance Graph

The following chart, produced by Research Data Group, Inc., depicts our performance for the period beginning December 31, 2015, and ending December 31, 2020, as measured by total stockholder return on our common stock compared with the total return of the NASDAQ Composite Index and a select group of peer companies comprised of NASDAQ-listed companies in SIC Code 6330-6339, Fire, Marine, and Casualty Insurance.

This performance graph is not incorporated into any other filing we have made with the U.S. Securities and Exchange Commission ("SEC") and will not be incorporated into any future filing we may make with the SEC unless we so specifically

incorporate it by reference. This performance graph shall not be deemed to be “soliciting material” or to be “filed” with the SEC unless we specifically request so or specifically incorporate it by reference in any filing we make with the SEC.

(f) Purchases of Equity Securities by the Issuer and Affiliated Purchasers

The following table provides information regarding our purchases of our common stock in the fourth quarter of 2020:

1We purchased these shares from employees to satisfy tax withholding obligations associated with the vesting of their restricted stock units.

2On December 2, 2020, we announced that our Board authorized a $100 million share repurchase program, which has no set expiration or termination date. Our repurchase program does not obligate us to acquire any particular amount of our common stock, and the repurchase program may be suspended or discontinued at any time at our discretion. The timing and amount of any share repurchases under the authorization will be determined by management at its discretion and based on market conditions and other considerations.

Item 6. Selected Financial Data.

Five-Year Financial Highlights1

Impact of catastrophe losses on combined ratio 8.0 pts 3.1 3.6 2.9 2.8

Yield on investments, after tax 2.6 % 2.9 2.8 2.1 1.9

Per common share data:

Net income available to common stockholders:

Price range of common stock:

Number of weighted average common shares:

1Refer to the Glossary of Terms attached to this Form 10-K as Exhibit 99.1 for definitions of terms used in these financial highlights.

2Beginning in 2018, changes in unrealized gains and losses on our equity portfolio are recognized in income through "Net realized and unrealized investment (losses) gains" on our Consolidated Statements of Income.

3Non-GAAP measure. Refer to the "Financial Highlights of Results Years Ended December 31, 2020, 2019, and 2018" in Item 7. "Management's Discussion and Analysis of Financial Condition and Results of Operations" of this Form 10-K for the definition.

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations.

Forward-looking Statements

Certain statements in this report, including information incorporated by reference, are “forward-looking statements” defined in the Private Securities Litigation Reform Act of 1995 (“PSLRA”). The PSLRA provides a safe harbor under the Securities Act of 1933, as amended, and the Exchange Act for forward-looking statements. These statements relate to our intentions, beliefs, projections, estimations or forecasts of future events or future financial performance and involve known and unknown risks, uncertainties and other factors that may cause us or the industry’s actual results, levels of activity, or performance to be materially different from those expressed or implied by the forward-looking statements. In some cases, you may identify forward-looking statements by use of words such as “may,” “will,” “could,” “would,” “should,” “expect,” “plan,” “anticipate,” “target,” “project,” “intend,” “believe,” “estimate,” “predict,” “potential,” “pro forma,” “seek,” “likely,” or “continue.” or other comparable terminology. These statements are only predictions, and we can give no assurance that such expectations will prove to be correct. We undertake no obligation, other than what federal securities laws may require, to publicly update or revise any forward-looking statements, regardless of new information, future events, or other unknowns.

Factors that could cause our actual results to differ materially from those projected, forecasted, or estimated in our forward-looking statements are discussed in further detail in Item 1A. “Risk Factors.” of this Form 10-K. These risk factors may not be exhaustive. We operate in a constantly changing business environment, and new risk factors may emerge at any time. We can neither predict these new risk factors nor assess their impact, if any, on our businesses or the extent any new factor or combination of factors may cause actual results to differ materially from any forward-looking statements. Given these risks, uncertainties, and assumptions, the forward-looking events we discuss in this report might not occur.

Introduction

We classify our business into four reportable segments:

•Standard Commercial Lines;

•Standard Personal Lines;

•E&S Lines; and

•Investments.

For more details about these segments, refer to Note 1. "Organization" and Note 12. "Segment Information" in Item 8. “Financial Statements and Supplementary Data.” of this Form 10-K.

We write our Standard Commercial and Standard Personal Lines products and services through nine of our insurance subsidiaries, some of which participate in the federal government's National Flood Insurance Program's ("NFIP") Write Your Own Program ("WYO"). We write our E&S products through another subsidiary, Mesa Underwriters Specialty Insurance Company, which provides us with a nationally-authorized non-admitted platform for customers who generally cannot obtain coverage in the standard marketplace. Collectively, we refer to our ten insurance subsidiaries as the "Insurance Subsidiaries".

The following is Management's Discussion and Analysis ("MD&A") of the consolidated results of operations and financial condition, as well as known trends and uncertainties, that may have a material impact in future periods. The MD&A discusses and analyzes our results in 2020 compared to 2019. Investors should read the MD&A in conjunction with Item 8. "Financial Statements." of this Form 10-K. For discussion and analysis of our 2019 results compared to 2018, refer to Item 7. "Management’s Discussion and Analysis of Financial Condition and Results of Operations." of our Annual Report on Form 10-K for the fiscal year ended December 31, 2019.

In the MD&A, we will discuss and analyze the following:

•Critical Accounting Policies and Estimates;

•Financial Highlights of Results for Years Ended December 31, 2020, 2019, and 2018;

•Results of Operations and Related Information by Segment;

•Federal Income Taxes;

•Financial Condition, Liquidity, and Capital Resources;

•Off-Balance Sheet Arrangements; and

•Contractual Obligations, Contingent Liabilities, and Commitments.

Critical Accounting Policies and Estimates

We have identified the policies and estimates critical to our business operations and the understanding of our results of operations. In preparing our consolidated financial statements ("Financial Statements"), we are required to make estimates and

assumptions that affect the reported amount of assets and liabilities, disclosure of contingent assets and liabilities at the date of our Financial Statements, and the reported amounts of revenue and expenses during the reporting period. We offer no assurances that actual results will be the same as those estimates, and it is possible they will differ materially. The policies and estimates we consider most critical to the preparation of the Financial Statements involved (i) reserves for loss and loss expense, (ii) investment valuations and the allowance for credit losses on available-for-sale ("AFS") fixed income securities, (iii) reinsurance, (iv) allowance for credit losses on premiums receivable, and (v) accrual for auditable premium.

Reserves for Loss and Loss Expense

Significant periods of time can elapse between the occurrence of an insured loss, the reporting of the claim to us, and the final settlement of the claim. To recognize liabilities for unpaid loss and loss expense, insurers establish reserves as balance sheet liabilities representing an estimate of amounts needed to pay reported and unreported net loss and loss expense. At December 31, 2020, we had recorded $4.3 billion of gross loss and loss expense reserves and $3.7 billion of net loss and loss expense reserves. At December 31, 2019, these gross and net reserves were $4.1 billion and $3.5 billion, respectively. The Insurance Subsidiaries' liability duration was approximately 3.7 years at December 31, 2020, up slightly from 3.6 years at December 31, 2019.

The following tables provide case and incurred but not reported (“IBNR”) reserves for loss and loss expenses, and reinsurance recoverable on unpaid loss and loss expense as of December 31, 2020 and 2019:

Loss and Loss Expense Reserves

1Includes general liability (95% of net reserves) and commercial auto liability coverages (5% of net reserves).

2Includes commercial property (92% of net reserves) and commercial auto property coverages (8% of net reserves).

Loss and Loss Expense Reserves

1Includes general liability (94% of net reserves) and commercial auto liability coverages (6% of net reserves).

2Includes commercial property (85% of net reserves) and commercial auto property coverages (15% of net reserves).

How reserves are established

Reserves for loss and loss expense includes case reserves on reported claims and reserves known as incurred but not reported ("IBNR") reserves. Case reserves are estimated on each individual claim, and based on claim-specific facts and circumstances known at the time. The case reserves may be adjusted upward or downward as the specific facts and circumstances change. IBNR reserves are established at more aggregated levels and include provisions for (i) claims not yet reported, (ii) future development on reported claims, (iii) previously closed claims that will be reopened in the future, and (iv) anticipated salvage and subrogation recoveries. For additional information on our accounting policy for reserves for loss and loss expense, refer to Note. 2. “Summary of Significant Accounting Policies” in Item 8. “Financial Statements and Supplementary Data.” of this Form 10-K.

Our robust reserve process relies upon internal reserve reviews performed quarterly, based upon our own loss experience, with consideration given to various internal and external factors. In addition to our internal reserve reviews, we have an external consulting actuary perform an independent review of our reserves semi-annually. We do not rely on the external consulting actuary's report for recording our reserves; however, we do review and discuss our respective observations regarding trends, key assumptions and actuarial methodologies. While not required to be performed by an independent external actuary, our independent external actuary issues the annual statutory Statements of Actuarial Opinion for our Insurance Subsidiaries.

Range of reasonable reserve estimates

We have estimated a range of reasonably possible reserve estimates for net loss and loss expense of $3,250 million to $3,893 million at December 31, 2020. This range reflects low and high reasonable reserve estimates determined by judgmentally adjusting the methods, factors and assumptions selected within the internal reserve review. This approach produces a range of reasonable reserve estimates, as opposed to a distribution of all possible outcomes. Therefore, it is possible that the final outcomes may fall above or below these amounts. The range does not include a provision for potential increases or decreases associated with asbestos, environmental, and certain other continuous exposure claims, which by their nature are more variable and, therefore, traditional actuarial techniques cannot be effectively applied.

The range of reasonable reserve estimates as of December 31, 2020 has expanded relative to December 31, 2019. This is partially due to the growth in reserves commensurate with our growth in net premiums earned ("NPE"), but also recognizes the additional risks in the reserve portfolio presented by the unique legislative, judicial, economic and social environment resulting from COVID-19. Some of these uncertainties may not be resolved for an extended period of time.

Changes in Reserve Estimates (Loss Development)

Our quarterly reserve process may lead to changes in the recorded reserves for prior accident years, which is referred to as favorable or unfavorable prior year loss and loss expense development. In 2020, we experienced net favorable prior year loss development of $72.9 million, compared to $50.3 million in 2019 and $29.9 million in 2018. The following table summarizes prior year development by line of business:

(Favorable)/Unfavorable Prior Year Loss and Loss Expense Development

General liability $ (35.0) (5.0) (9.5)

Businessowners' policies 3.9 1.9 (1.5)

Commercial property 9.2 5.1 7.5

Personal automobile (1.8) 4.4 3.0

E&S casualty lines — 2.0 12.0

E&S property lines (4.0) 1.0 (4.8)

A detailed discussion of recent reserve development by line of business follows.

Standard Market General Liability Line of Business

At December 31, 2020, our general liability line of business had recorded reserves, net of reinsurance, of $1.4 billion, which represented 38% of our total net reserves. In 2020, this line experienced favorable development of $35.0 million, attributable to lower loss severities in accident years 2017 and prior.

During 2019, this line experienced favorable development of $5.0 million, attributable to lower loss severities in accident years 2015 and 2016, partially offset by increases in the 2017 and 2018 accident year.

By its nature, this line presents a diverse set of exposures. General liability losses and loss trends are influenced by a variety of factors, including legislative enactments, judicial decisions, and economic and social inflation. Economic inflation directly impacts our claims severities, such as increasing costs of raw materials, medical procedures and labor costs. Social inflation may impact both the frequency and severity of claims by impacting (i) the propensity for a claimant to file a claim, (ii) the percentage of claimants who engage lawyers, and (iii) the nature of judicial verdicts and amount of the associated awards.

We have exposure to abuse or molestation claims through insurance policies that we (i) principally underwrite through our Community and Public Services ("CAPS") strategic business unit and (ii) issue to schools, religious institutions, day-care facilities, and other social services. Through 2017, our exposure to abuse or molestation risk had been increasing, reflective of the growth in our CAPS book. In 2018, we introduced more stringent underwriting eligibility guidelines and partnered with a third party to better assess exposure and introduce greater loss control measures. In 2019, we filed and approved significant rate increases for this exposure. These actions have limited our growth in this strategic business unit.

We also have exposure to abuse or molestation claims from recently enacted state laws that extend the statute of limitations or permit windows for abuse or molestation claims and lawsuits to be filed that statutes of limitations previously barred. Consequently, we may receive claims decades after the alleged acts occurred for policies issued by predecessor companies that will involve complex claims coverage determinations, potential litigation, and the need to collect from reinsurers under older reinsurance agreements.

To better understand our exposure to abuse or molestation, we have instituted enhanced claims coding to identify and classify abuse or molestation claims. Our claims and actuarial departments actively monitor these claims to identify changes in frequency or severity and any emerging or shifting trends. While these actions should help us better understand this rapidly evolving exposure, the ultimate impact of social, political, and legal trends remains highly uncertain, and — as a result — our loss and loss expense reserves remain highly uncertain.

The COVID-19 pandemic presents additional risk to this line in several forms. First, as businesses reopen, they may be susceptible to claims alleging customers contracting COVID-19 due to unsafe business practices. Hiring practices may also be called into question as businesses re-staff. In addition to COVID-19-specific claims, changes in claims reporting or settlement

practices may have been, and may continue to be, affected by several factors, including individual's propensity to bring a claim during the shut-down, court closures, and other behavioral and procedural changes.

Standard Market Workers Compensation Line of Business

At December 31, 2020, our workers compensation line of business recorded reserves, net of reinsurance, of $870 million, which represented 23% of our total net reserves. During 2020, this line experienced favorable development of $60.0 million, driven by accident years 2018 and prior. During 2019, this line experienced favorable development of $68.0 million, driven by accident years 2017 and prior. During both 2020 and 2019, this line experienced lower loss emergence than expected, due, in part, to: (i) lower medical inflation than originally anticipated; (ii) our proactive underwriting actions; and (iii) various significant claims initiatives that we have implemented. Because of the length of time that injured workers receive medical treatment, decreases in medical inflation can cause favorable loss development across an extended number of accident years.

While we believe the underwriting and claims operational changes improved our underwriting experience, there is also risk associated with change. Most notably, changes in operations may inherently change paid and reported development patterns. While our reserve analyses incorporate methods that adjust for these changes, there remains a greater risk of fluctuation in the estimated reserves.

In addition to the uncertainties associated with our actuarial assumptions and methodologies, the workers compensation line of business can be impacted by a variety of other issues, such as the following:

Unexpected changes in medical cost inflation - The industry is currently experiencing a period of lower claim cost inflation. Changes in our historical workers compensation medical costs, along with uncertainty regarding future medical inflation, creates the potential for additional variability in our reserves;

Changes in statutory workers compensation benefits - Benefit changes may be enacted that affect all outstanding claims, including claims that have occurred in the past. Depending upon the social and political climate, these changes may either increase or decrease associated claim costs;

Changes in utilization of the workers compensation system - These changes may be driven by economic, legislative, or other changes, such as increased use of pharmaceuticals, more complex medical procedures, changes in the life expectancy of permanently-injured workers, and availability of health insurance, among others.

COVID-19-related impacts - While we are not a major insurer of front-line workers (e.g. medical, hospital, etc.), we do have potential exposure to employees contracting COVID-19 in the course of their employment. These claims may be asserted under "presumption statutes" implemented by certain states, shifting the burden of proof from the claimant to the insurer. Furthermore, the significant impact to unemployment, coupled with injured workers delaying non-essential procedures, may extend the duration of non-COVID-19 claims.

Standard Market Commercial Automobile Line of Business

At December 31, 2020, our commercial automobile line of business had recorded reserves, net of reinsurance, of $645 million, which represented 17% of our total net reserves. In 2020, this line experienced unfavorable prior year development of $7.1 million, driven by higher loss severities in accident years 2016 through 2019 and higher than expected frequencies in accident year 2019. In 2019, this line experienced no material prior year reserve development. For both us and the industry, the commercial automobile line had experienced unfavorable trends in recent years. Increased frequencies were likely due to increased miles driven as a result of lower unemployment and lower gasoline prices, coupled with poor road quality, as well as an increase in distracted driving. The onset of the COVID-19 pandemic in early 2020, along with governmental "stay-at-home" orders, dramatically reduced miles driven and road traffic, significantly reducing claims frequency. While miles driven has increased, activity remains modestly below expected levels. Conversely, both entering the pandemic and post-pandemic, we have seen rising severities on both bodily injury and property damage claims. The average value of our bodily injury paid loss settlements has increased, which may relate to a trend we have seen of more claimants using attorneys in the claims process. Increasing property damage severities may be tied to the increased repair costs for increasingly complex vehicles that incorporate more technology. These trends may be further exacerbated during the economic slow-down, where less vehicles were on the road, but driving at higher speeds.

Over the last several years, we have taken actions to improve the profitability of this line of business, including:

•Taking meaningful rate and underwriting actions on our renewal portfolio. We will continue to leverage our predictive modeling and analytical capabilities to provide more granular insights about where we should focus our actions.

•Aggressively managing new business pricing and hazard mix, co-underwriting selected higher hazard classes by the field and home office, providing better recognition of risk drivers, and improved pricing.

•Reducing premium leakage by improving the quality of our rating information. This includes validating application information using third-party data and obtaining more detailed driver information.

•Implementing new tools to score drivers to underwrite more effectively and align rate with exposure.

Standard Market Personal Automobile Line of Business

At December 31, 2020, our personal automobile line of business had recorded reserves, net of reinsurance, of $98 million, which represented 3% of our total net reserves. In 2020, this line experienced favorable prior year reserve development of $1.8 million, mainly attributable to lower loss severities in accident year 2019. In 2019, this line experienced unfavorable prior year reserve development of $4.4 million, mainly attributable to higher loss severities in accident year 2018.

Some of the same issues affecting the commercial automobile line are also affecting this line. Furthermore, the COVID-19-related impact of reduced frequency was more pronounced in this line, with similar potential for higher average severities. Aside from the COVID-19-related temporary impacts, the underlying trends of increased miles driven and vehicle repair costs, poor road quality, and distracted driving, are likely causes of increased frequencies and rising severities. We continue to recalibrate our predictive models and refine our underwriting and pricing approaches. While we believe these changes will ultimately lead to improved profitability and greater stability, the resulting changes to our exposure profile may impact paid and reported development patterns, thereby increasing the uncertainty in the reserves in the near-term.

E&S Casualty Lines of Business

At December 31, 2020, our E&S casualty lines of business had recorded reserves, net of reinsurance, of $405 million, which represented 11% of our total net reserves. Our E&S casualty lines results have improved over recent years. Our E&S casualty lines underwriting operations have exited several targeted classes of business that historically have produced volatile results, including commercial auto liability, liquor liability, and snow removal. While we continue to build historical loss experience in this segment, its history remains more limited than for our Standard Commercial Lines segment. Furthermore, the composition of the E&S book has changed over time, which may impact loss and loss expense development patterns. These factors increase the uncertainty in the reserve estimates for this line.

Recent E&S casualty claims actions have created further casualty improvements:

•In 2020, we created a dedicated E&S claims team within our corporate claims function to bring greater expertise and consistency to E&S claims handling.

•Claims have been segregated into “litigated” and “non-litigated” categories, separate teams with specialized skill sets handling each category.

•We implemented the following operational and expense improvement initiatives for outside adjusters and legal counsel:

◦Maximized use of staff counsel, increasing staff where necessary to support claims volume;

◦Heightened focus on legal budgeting and expense management; and

◦Implemented a panel counsel review process.

We believe that these actions identify severe claims earlier, create earlier claims resolutions, and improve outcomes. However, claims operation changes can impact claims reserving and settlement patterns. Reserve estimate uncertainty increases after claims operational changes because it takes time for the patterns to stabilize.

Other impacts creating additional loss and loss expense reserve uncertainty

Claims Initiative Impacts

Consistent with our strategic imperative to optimize operational efficiency, our Claims Department is continually identifying areas for improvement and efficiency to increase our value proposition to policyholders. These improvements may lead to changes in claims practices that affect average case reserve levels and claims settlement rates, which directly impact the data used to project ultimate loss and loss expense. While these changes may increase uncertainty in our estimates in the short term, we expect refined management of the claims process to be the longer-term benefit.

COVID-19 presented some unique dynamics within our Claims department. Particularly during the early part of the pandemic, with less new claims being reported, the claims department placed greater focus on the existing claims inventory, leading to a speed-up of claim closures. This speed-up stabilized over the course of the year, with closure rates returning closer to pre-pandemic levels.

Our internal reserve analyses incorporate certain actuarial projection methods that make adjustments for changes in case reserve adequacy and claims settlement rates. These methods adjust our historical loss experience to the current level of case adequacy

or settlement rate, which provides a more consistent basis for projecting future development patterns. These methods have their own associated assumptions and judgments and, like any projection method, are not definitive in and of themselves.

Economic Inflationary Impacts

United States ("U.S.") monetary policy and global economic conditions may bring additional uncertainty related to inflationary trend. Changes in inflation affect the ultimate settlement costs for many of our lines of business, with the greatest impact in the longer-tailed lines such as general liability and workers compensation. Therefore, uncertainty about future inflation or deflation creates the potential for additional reserve variability in these lines of business.

Sensitivity analysis: Potential impact on reserve uncertainty due to changes in key assumptions

Our process to establish reserves includes a variety of key assumptions, including without limitation:

•The selection of loss and loss expense development factors;

•The weight to be applied to each individual actuarial projection method;

•Projected future loss trends; and

•Expected claim frequencies, severities, and ultimate loss and loss expense ratios for the current accident year.

The importance of any single assumption depends on several considerations, such as the line of business and the accident year. If the actual experience emerges differently than the assumptions used in the process to establish reserves, changes in our reserve estimate are possible that may be material to the results of operations in future periods. Below are sensitivity tests that highlight potential impacts to loss and loss expense reserves for the major casualty lines of business under different scenarios. These tests consider each assumption and line of business individually, without any consideration of correlation between lines of business and accident years. Therefore, the results do not constitute an actuarial range. While the figures represent possible impacts from variations in certain key assumptions, there is no assurance that future loss and loss expense emergence will be consistent with either our current or alternative sets of assumptions.

While the sources of reserve variability are generated by different internal and external trends and operational changes, they ultimately manifest themselves as changes in the expected loss and loss expense development patterns. These patterns are a key assumption in the reserving process. In addition, the current accident year expected loss and loss expense ratios are also a key assumption. These ratios are developed through a rigorous process of projecting recent accident years' experience to an ultimate settlement basis, and then adjusting them to the current accident year's pricing and loss cost levels. Impact from changes in the underwriting portfolio and to claims handling practices are also quantified and reflected where appropriate. As with all estimates, the ultimate loss and loss expense ratios may differ from those currently estimated.

The sensitivities of loss and loss expense reserves to these key assumptions are illustrated below for the major casualty lines. The first table displays estimated impacts from changes in expected reported loss and loss expense development patterns for our major casualty lines of business. It shows reserve impacts by line of business if the actual calendar year incurred amounts are greater or less than current expectations by the selected percentages. While the selected percentages by line are judgmental, they are based on the reserve range analysis and the actual historical reserve development for the line of business. The second table displays the estimated impacts from changes to the expected loss and loss expense ratios for the current accident year. It shows reserve impacts by line of business if the expected loss and loss expense ratios for the current accident year are greater or less than current expectations by the selected percentages.

Reserve Impacts of Changes to Expected Loss and Loss Expense Reporting Patterns

Commercial automobile liability 15 (80) 80

Personal automobile liability 15 (10) 10

General liability 10 pts $ (70) $ 70

Workers compensation 10 (30) 30

Commercial automobile liability 10 (45) 45

Personal automobile liability 10 (10) 10

Note that there is some overlap between the impacts in the two tables. For example, increases in the calendar year development would ultimately impact our view of the current accident year's loss and loss expense ratios. However, these tables provide perspective on the sensitivity of each key assumption. While the changes represent outcomes based on reasonably likely changes to our underlying reserving assumptions, they do not represent a full range of possible outcomes. Our reserves could increase or decrease significantly more or significantly less than what the tables above reflect.

Asbestos and Environmental Reserves

Our general liability, excess liability, and homeowners reserves include exposure to asbestos and environmental claims. The emergence of these claims occurs over an extended period and is highly unpredictable. The total recorded net loss and loss expense reserves for these claims were $21.4 million as of December 31, 2020 and $21.6 million as of December 31, 2019.

“Environmental claims” are claims alleging bodily injury or property damage from pollution or other environmental contaminants other than asbestos. Our exposure to environmental liability is primarily due to (i) landfill exposures from policies written prior to the absolute pollution endorsement in the mid 1980s; and (ii) residential underground storage tank leaks, mainly in New Jersey. The landfill claims stem primarily from insured exposures in municipal government, and small non-manufacturing commercial risks. Some of these claims relate to specific landfill sites on the National Priorities List (“NPL”) by the United States Environmental Protection Agency (“USEPA”). We currently have reserves for six policyholders related to three NPL sites. The underground storage tank claims relate largely to our homeowners policies.In 2007, we introduced a fuel oil system exclusion on our New Jersey homeowners policies that greatly limited this exposure from that point forward.

“Asbestos claims” are claims for bodily injury alleged to have occurred from exposure to products containing asbestos. Our primary exposure arises from policies issued to various distributors of asbestos-containing products, such as electrical and plumbing materials. At December 31, 2020, asbestos claims constituted 23% of our $21.4 million net asbestos and environmental reserves, compared to 23% of our $21.6 million net asbestos and environmental reserves at December 31, 2019.

Our asbestos and environmental claims are handled in our centralized and specialized asbestos and environmental claim unit. That unit establishes case reserves on individual claims based upon the facts and circumstances known at a given point in time, which are supplemented by bulk IBNR reserves.

Estimating IBNR reserves for asbestos and environmental claims is difficult because these claims have delayed and inconsistent reporting patterns. In addition, there are significant uncertainties associated with estimating critical reserve assumptions, such as average clean-up costs, third-party costs, potentially responsible party shares, allocation of damages, litigation and coverage costs, and potential state and federal legislative changes. Prior to the introduction of the absolute pollution exclusion endorsement in the mid-1980's, we primarily wrote Standard Personal Lines, which has limited our exposure to asbestos and environmental claims.

Other Latent Exposures

We also have other latent and continuous trigger exposures in our ongoing portfolio. Examples include claims for construction defect and abuse or molestation, for which states have increased and expanded the statute of limitations. We manage our exposure to these liabilities through our underwriting and claims practices and, like asbestos and environmental claims, a dedicated claims unit handles these claims. The impact of social, political, and legal trends on these claims remains highly uncertain, so our loss and loss expense reserves on these claims remain highly uncertain. These exposures remain in our ongoing portfolio, and as such, are reserved in aggregate, with other exposures within the line of business reserves.

Investment Valuation and the Allowance for Credit Losses on AFS Fixed Income Securities

Investment Valuation

The fair value of our investment portfolio is defined under accounting guidance as the exit price or the amount that would be (i) received to sell an asset or (ii) paid to transfer a liability in an orderly transaction between market participants. When determining an exit price we must, when available, rely on observable market data. The majority of securities in our equity portfolio have readily determinable fair values and are recorded at fair value with changes in unrealized gains or losses recognized through income. Our available-for-sale ("AFS") fixed income securities portfolio is recorded at fair value, and the related unrealized gains or losses are reflected in stockholders' equity, net of tax. For our AFS fixed income securities portfolios, fair value is a key factor in the measurement of (i) losses on securities for which we have the intent to sell, and (ii) changes in the allowance for credit losses.

We have categorized our investment portfolio, based on the priority of the inputs to the valuation technique, into a three-level fair value hierarchy. The fair value hierarchy gives the highest priority to quoted prices in active markets for identical assets and liabilities (Level 1), the next level of priority to observable data from similar securities that have traded in the marketplace, typically using matrix pricing (Level 2), and the lowest priority to unobservable inputs (Level 3).

The fair value of approximately 98% of our investments measured at fair value are classified as either Level 1 or Level 2 in the fair value hierarchy. Fair value measurements in Level 1 represent quoted prices in active markets for identical assets. The fair value of our Level 2 securities are determined by external pricing services, for which we have evaluated the pricing methodology used and determined that the inputs used are observable. Less than 2.0% of our investments measured at fair value are classified as Level 3 in the fair value hierarchy. Fair value measurements in Level 3 are based on unobservable market inputs because the related securities are not traded on a public market. For additional information regarding the valuation techniques used for our Level 3 securities, refer to item (d) of Note 2. "Summary of Significant Accounting Policies" within Item 8. "Financial Statements and Supplementary Data." of this Form 10-K.

Allowance for Credit Losses on AFS Fixed Income Securities

When fixed income securities are in an unrealized loss position and we do not intend to sell the security, we record an allowance for credit losses for the portion of the unrealized loss due to an expected credit loss. We estimate expected credit losses on these securities by performing a discounted cash flow (“DCF”). The allowance for credit losses is the excess of amortized cost over the greater of (i) our estimate of the present value of expected future cash flows, or (ii) fair value. The allowance for credit losses cannot exceed the unrealized loss and therefore it may fluctuate with changes in the fair value of the security.

Factors considered in the determination of the allowance for credit losses require significant judgment and include, but are not limited to, our evaluation of the projected cash flow stream from the security. We also consider the need to record losses on securities for which we have the intent to sell that are in an unrealized loss position.

The various COVID-19-related governmental directives impacted the financial markets, which became volatile earlier in the year. This volatility increased gross unrealized losses on our AFS fixed income securities portfolio from $7.7 million at December 31, 2019, to $116.9 million at March 31, 2020. Since the end of the first quarter, the financial markets have improved and gross unrealized losses were reduced to $11.5 million at December 31, 2020. We analyzed these unrealized losses for credit loss in accordance with our existing accounting policy, which includes performing DCF analyses on each security at the lot level and analyzing these DCFs using various economic scenarios. In performing these DCF analyses, we calculate the present value of future cash flows using various models specific to the major security types in our portfolio. These models use security-specific information and forecasted macroeconomic data to determine possible expected credit loss scenarios based on projected changes in the economy. The forecasted economic data incorporated in the models is based on the Federal Reserve Board’s annual supervisory stress test review on certain large banks and financial institutions. We also have the ability to incorporate internally-developed forecast information into the models as we deem appropriate. In developing our best estimate of the allowance for credit losses, we consider our outlook as to the probability of the various scenarios occurring.

Based on these analyses, we recorded an allowance for credit losses of $4.0 million in 2020 on our AFS fixed income portfolio. After considering the allowance for credit losses, the remaining unrealized losses on this portfolio was $11.5 million. We believe that the volatility and increased unrealized loss balance was driven by fluctuating and widening credit spreads tied to financial market uncertainty about the various COVID-19-related governmental directives. If the assumptions used in our DCF analyses or our outlook as to the occurrence probability of our DCF model scenarios were to change, our allowance for credit losses and the resulting credit loss expense could be material to our results of operations.

For additional information regarding our allowance for credit losses on AFS fixed income securities, see item (c) of Note 2. "Summary of Significant Accounting Policies" and item (i) of Note 5. "Investments" within Item 8. "Financial Statements and Supplementary Data." of this Form 10-K, respectively.

Reinsurance

Reinsurance recoverables on paid and unpaid loss and loss expense represent estimates of the portion of such liabilities that we will recover from reinsurers. Each reinsurance contract is analyzed to ensure that sufficient risk is transferred to properly record the transactions as reinsurance in the Financial Statements. Amounts recovered from reinsurers are recognized as assets contemporaneously and in a manner consistent with, the paid and unpaid losses associated with the reinsured policies. An allowance for credit losses on our reinsurance recoverable balance is recorded based on an evaluation of balances due from reinsurers and other available information. However, reinsurers often purchase and rely on their own retrocessional reinsurance programs to manage their capital position and improve their financial strength ratings. Details regarding retrocessional reinsurance programs are not always transparent, which can make it difficult to assess our reinsurers' exposure to counterparty credit risk. The credit quality of our reinsurers is also impacted by other factors, such as their reserve adequacy, investment portfolio, regulatory capital position, catastrophe aggregations, and risk management expertise. In addition, contractual language interpretations and willingness to pay valid claims can impact our allowance for estimated uncollectible reinsurance. Our allowance for estimated uncollectible reinsurance totaled $1.8 million at December 31, 2020, a decrease from $4.4 million at December 31, 2019, as we refined our methodology and implemented the new credit loss standard in 2020. We continually monitor developments that may impact recoverability from our reinsurers, for which we have contractual remedies if necessary. For further information regarding reinsurance, see the “Reinsurance” section below and Note 9. “Reinsurance” in Item 8. “Financial Statements and Supplementary Data.” of this Form 10-K.

Allowance for Credit Losses on Premiums Receivable

We estimate an allowance for credit losses on our outstanding premiums receivable balance at each reporting date. In determining this allowance, we use a method that considers the aging of the receivable based on the effective year of the related policy and our historical credit loss experience. We also contemplate expected macroeconomic conditions over the expected receivables collection period, which is short-term in nature because most balances are collected within two years of policy issuance. We increased our allowance for credit losses to $21.0 million during 2020 from $6.4 million at December 31, 2019, to reflect (i) the higher risk of non-payment due to the significant COVID-19-related decline in economic activity, (ii) the individualized payment flexibility we offered our customers, and (iii) our suspension of the effect of policy cancellations, late payment notices, and late or reinstatement fees. Our last suspensions expired in early August 2020. It could take over a year to realize this collections process, and we expect the actual reserve write-offs to materialize over the course of 2021.

Future COVID-19-related economic instability or governmental directives could ultimately impact our estimates and assumptions for credit losses on premiums receivable. Consequently, a change in our allowance estimate may be material to our results of operations in future periods. For additional details about this estimate, see Note 8. "Allowance for Credit Losses on Premiums Receivable" in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K.

Accrual for Auditable Premium

We estimate auditable premium, which we either bill or return on expired policies based on exposure levels (i.e. payroll or sales), when it is reasonably possible to do so based on historical trends adjusted for the uncertainty of future economic conditions. If we determine it is not reasonably possible to estimate this premium, we do not do so. In the first quarter of 2020, we recorded a $75 million return audit and mid-term endorsement premium accrual in response to the COVID-19 pandemic and the anticipated decline in payroll and sales exposures on the workers compensation and general liability lines of business. During the remainder of the year, we applied premium adjustments for endorsements and audits against our accrual, resulting in a remaining $24.8 million accrual as of December 31, 2020. We currently anticipate the balance of the return audit premiums will occur through the middle of 2021. Since April 2020, through active engagement between our underwriters, distribution partners, and insureds, we have set exposure levels to reflect our best estimate of how the current environment may impact our policies. As a result, we have not accrued for additional or return premium on any policies since that time. Further economic instability and renewed or extended COVID-19-related governmental directives ultimately could impact our estimates and assumptions, and consequently, changes in this liability estimate may be material to the results of operations in future periods. For additional details about this estimate, see Note 9. "Reinsurance" in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K.

Financial Data:

Key Metrics:

Return on average common equity ("ROE") 10.4 % 13.6 (3.2) pts 10.2 3.4 pts

Per Common Share Amounts:

Dividends declared per share to common stockholders 0.94 0.83 13 0.74 12

Non-GAAP Information:

Diluted non-GAAP operating income per common share2 4.15 4.40 (6) 3.66 20

1Refer to the Glossary of Terms attached to this Form 10-K as Exhibit 99.1 for definitions of terms used in this financial review.

2Non-GAAP operating income is a measure that is comparable to net income available to common stockholders with the exclusion of after-tax net realized and unrealized gains and losses on investments, and after-tax debt retirement costs. Non-GAAP operating income is used as an important financial measure by us, analysts, and investors because the realization of investment gains and losses on sales of securities in any given period is largely discretionary as to timing. In addition, net realized and unrealized investment gains and losses on investments that are charged to earnings and the debt retirement costs could distort the analysis of trends.

Reconciliations of net income available to common stockholders, net income available to common stockholders per diluted common share, and ROE to non-GAAP operating income, non-GAAP operating income per diluted common share, and non-GAAP operating ROE, respectively, are provided in the tables below:

Net realized and unrealized losses (gains), before tax 4,217 (14,422) 54,923

Debt retirement costs, before tax — 4,175 —

Net realized and unrealized losses (gains), before tax 0.07 (0.24) 0.92

Debt retirement costs, before tax — 0.07 —

Non-GAAP operating income per diluted common share $ 4.15 4.40 3.66

Reconciliation of ROE to non-GAAP operating ROE 2020 2019 2018

Net realized and unrealized losses (gains), before tax 0.2 (0.7) 3.1

Debt retirement costs, before tax — 0.2 —

Tax on reconciling items (0.1) 0.2 (0.8)

The components of our ROE are as follows:

Standard Commercial Lines Segment 5.1 % 5.8 (0.7) 4.9 0.9

Standard Personal Lines Segment (0.5) 0.3 (0.8) 0.6 (0.3)

E&S Lines Segment — 0.4 (0.4) — 0.4

Net realized and unrealized (losses) gains (0.1) 0.5 (0.6) (2.3) 2.8

Debt retirement costs — (0.2) 0.2 — (0.2)

In 2020, we generated a 10.5% non-GAAP operating ROE, which fell slightly below our 11% target for the year and our 2019 return of 13.3%. Our 2020 non-GAAP operating ROE was negatively impacted by net unrealized after-tax gains on our fixed income securities portfolio, which increased our GAAP equity and decreased our non-GAAP operating ROE by approximately 120 basis points. Nevertheless, we consider this an impressive result in the context of COVID-19, significant catastrophe loss activity, and a prolonged low interest rate environment that has continued to put downward pressure on our investment portfolio returns. The following is a more detailed discussion of these items.

COVID-19

•A $75 million return audit and mid-term endorsement premium accrual recorded in the first quarter of 2020 to reflect our estimate of reduced exposures on our March 31 inforce policies due to the significant economic slowdown and the anticipated decline in payroll and sales exposures in the workers compensation and general liability lines of business. During the remainder of the year, we recorded $50.2 million of mid-term endorsement and negative audit premium adjustments against this $75 million accrual. As of December 31, 2020, we had a remaining accrual of $24.8 million. Net of reduced losses and commissions, the earned impact of the return audit and mid-term endorsement premium accrual lowered pre-tax underwriting results by $15.3 million, in 2020.

•A $19.7 million reduction in net premiums written ("NPW") recorded in the second quarter of 2020 to reflect a then voluntary credit to our personal and commercial automobile customers with in-force policies equivalent to 15% of their April and May premiums due to the unprecedented nature of the COVID-19-related governmental directives and the associated favorable claims frequency impact. During the second quarter of 2020, the premium credits were offset by an equal reduction in loss and loss expenses, as claims frequency on our personal and commercial automobile lines of business declined due to governmental directive-induced reduced miles driven. As the number of vehicles we insure has not significantly declined, frequencies are returning closer to normal levels as the COVID-19-related governmental directives terminate and there is uncertainty about potential impacts to severities.

•A $13.5 million, pre-tax, increase to our allowance for credit losses on premiums receivable reflecting an increase in credit risk due to billing accommodations that we offered our customers, sometimes in collaboration with or at the direction of our regulators. These accommodations included individualized payment flexibility and suspended the effect of policy cancellations, late payment notices, and late or reinstatement fees. The impact of offering billing accommodations while suspending cancellations increased earned but uncollected premiums. The majority of these state regulations have expired as of the end of 2020; however, our allowance for credit losses on premiums receivable of $21.0 million is expected to cover anticipated write-offs that will occur over the corresponding collections cycle, which could last more than a year.

•A $5.0 million, pre-tax, ultimate net loss estimate for losses related to a small portion of our property policies that provide a $25,000 sub-limited coverage for specified extra expenses to clean or disinfect a property when ordered by a Board of Health.

Overall, these four items (i) reduced pre-tax underwriting results by $33.8 million, or $0.44 per diluted common share, (ii) increased the combined ratio by 1.1 points, and (iii) decreased our ROE by 1.1 points.

Offsetting these COVID-19 specific items was a lower level of reported claim frequencies due to the reduced economic activity and other factors. These lower frequencies directly impacted our property lines loss experience. The impact of these lower than expected non-catastrophe property losses (including automobile physical damage losses) resulted in an approximate 1.2 point benefit to our combined ratio. We also reduced our 2020 commercial and personal auto casualty loss costs to partially reflect these lower frequencies for these shorter-tail lines of business, which benefited the combined ratio by 0.4 points. No other casualty lines were adjusted. These modest adjustments to our casualty loss estimates recognize the ongoing inherent uncertainty presented by COVID-19, including the potential for late reported claims and higher severities. We will continue to monitor these trends as we progress through 2021. After March 2020, due to the impact of COVID-19, we suspended business travel and entertainment in most of our regions. We also deferred some projects and new hires for a period of time. These items, which we expect to revert back to more normal levels later in 2021, benefited our 2020 expense ratio by approximately 0.7 points.

In total, we estimate the impact of the lower non-catastrophe property losses, the reduction in our loss ratio due to lower miles driven, and the benefit to the expense ratio all discussed above, collectively more than offset the negative impact from the COVID-19 specific accruals. We estimate the net benefit to our 2020 combined ratio was approximately 1.2 points.

Catastrophe Losses

We experienced a significant level of catastrophe losses in 2020, driven by industry-wide U.S. catastrophe loss activity that significantly exceeded the 5- and 10-year historical means of approximately 4 points. Catastrophes included hurricanes, with several making landfall, convective storms, hail storms, wildfires, and civil unrest. Our combined ratio in 2020 included 8.0 points of catastrophe losses, which was close to our highest level in over 20 years. The $215.4 million of catastrophe losses in 2020 compared to $81.0 million in 2019 reduced net income by $106.2 million, and ROE by 4.5 points.

Investment Portfolio Returns

After-tax investment income increased 2% in 2020 compared to 2019, driven by higher returns on alternative investments in our other investment portfolio. Returns on these holdings are recorded on a one-quarter lag, and the strong capital market performance in the second and third quarters of 2020 drove the higher returns. These returns, coupled with (i) operating cash flows that were 20% of 2020 NPW and (ii) proceeds from our preferred stock offering, increased invested assets by 12% during 2020. However, the increase in invested assets did not keep pace with the increase in common stockholders' equity. Accordingly, investment leverage declined, as reflected in invested assets per dollar of common stockholders' equity, which ended 2020 at $2.96, down from $3.05 at December 31, 2019. After-tax portfolio yields also were lower than a year ago, at 2.6% for 2020 compared to 2.9% for 2019, driven by a lower interest rate environment. The reduced investment leverage, coupled with lower portfolio yields, has resulted in a lower investment income contribution to ROE, which was 7.8% in 2020 compared to 9.1% in 2019.

Despite the significant economic impacts described above, we experienced favorable prior year casualty reserve development of $85 million in 2020 compared to $61 million in 2019, which is discussed in more detail in the "Insurance Operations" section of "Results of Operations and Related Information by Segment" below.

In 2020, we generated our seventh consecutive year of double-digit non-GAAP operating ROEs, with a 10.5% non-GAAP operating ROE. We also grew book value per common share 15% in 2020 compared to 2019, reflecting $4.09 per diluted common share of net income available to common stockholders and $2.25 per diluted common share of after-tax net unrealized gains on our fixed income securities portfolio that were partially offset by $0.94 per diluted common share of dividends paid to common stockholders.

On December 2, 2020, we issued $200 million of 4.60% non-cumulative perpetual preferred stock, which marks the first preferred stock offering in our 94-year history and is a demonstration of our investors' confidence in our value proposition and our continued success. In conjunction with this offering, our Board of Directors ("Board") authorized a $100 million share repurchase program. We intend to be disciplined and opportunistic with our buyback program, repurchasing shares when we believe returns are attractive over the long-term for our shareholders.

Outlook

For 2021, we established a non-GAAP operating ROE target of 11%, which is in line with our 2020 target. We based our 2021 target on our current estimated weighted average cost of capital, the current interest rate environment, and property and casualty insurance market conditions. Our ROE target sets a high bar for our financial performance, challenges us to perform at our best, and aligns our incentive compensation structure with shareholder interests. We enter 2021 in the strongest financial position in our Company's long history, and we are very well positioned to continue delivering growth and profitability.

Looking ahead to 2021, a number of areas require our continued focus to position us for ongoing success:

•Delivering on our strategy for continued disciplined growth, driven by greater share of wallet in our agents’ offices, the addition of new agents, and geographic expansion over the longer term. We continue to work to achieve our longer-term Standard Commercial Lines 3% market share target in our 27 primary operating states, which represents an additional $3 billion premium opportunity. Our strategy is to appoint distribution partners representing approximately a 25% market share and seeking an average 12% share of wallet, or percentage of these partners' books of business. In addition, we anticipate re-starting our geographic expansion strategy. The five states that we opened during 2017 and 2018, including a new Southwest region, are all performing ahead of expectations. Over the next two years, we plan to open three additional states subject to regulatory approval, Idaho, Vermont, and Alabama, , and we plan to open others in subsequent years. Our long-term goal is to have national capabilities, although we will follow a measured and disciplined approach to identifying and opening new markets.

•Continuing to achieve written renewal pure price increases that meet or exceed expected loss trend, while delivering

on our strategy for continued disciplined growth. While we continue to navigate a challenging economic environment, we are comfortable with the overall price adequacy of our book of business.

•Delivering a superior omnichannel customer experience by offering value-added technologies and services. We have significantly enhanced our customer experience capabilities over the last several years, and we provide our customers with various digital and self-service offerings. Investing in and building out technologies that improve the customer experience journey remains a core focus for us.

•Building a culture that fosters innovation and idea generation that is centered on the values of diversity, equity and inclusion, as we seek to develop a group of specially trained leaders to take our company into the future.

For 2021, our full-year guidance is as follows:

•A GAAP combined ratio, excluding catastrophe losses, of 91.0%. This assumes no prior-year casualty reserve development;

•Catastrophe losses of 4.0 points;

•After-tax net investment income of $182 million, which includes $16 million after-tax gains from our alternative investments;

•An overall effective tax rate of approximately 20.5%, which also includes an effective tax rate of 19.0% for net investment income and 21% for all other items; and

•Weighted average shares outstanding of 60.5 million on a diluted basis.

Results of Operations and Related Information by Segment

Insurance Operations

The following table provides quantitative information for analyzing the combined ratio:

Insurance Operations Results:

Less:

Combined Ratios:

Dividends to policyholders ratio 0.1 0.2 (0.1) 0.3 (0.1)

Our NPW increased 3% in 2020 compared to 2019, reflecting (i) overall renewal pure price increases of 4.3%, (ii) increased retention, and (iii) new business of $579.7 million in 2020 compared to $548.7 million in 2019. The net appointment of 42 retail agents, excluding agency consolidations, also contributed to our new business growth. This solid growth in a challenging economic environment reflects the strong relationships we have with our best-in-class distribution partners, our sophisticated underwriting and pricing tools, and excellent customer servicing capabilities.

The rate of NPW growth in 2020 was negatively impacted by approximately 4 percentage points due to the following:

•Our $75 million estimate of audit and endorsement return premium related to lower payroll and sales exposures on the workers compensation and general liability lines of business resulting from the economic impacts of the COVID-19 pandemic.

•A $19.7 million premium credit to our personal and commercial automobile policyholders. Because of the unprecedented nature of the COVID-19-related governmental directives and the associated expected short-term favorable claims frequency impact, we obtained regulatory approval during April to provide this premium credit to our personal and commercial automobile customers. The premium credit to customers with in-force policies was equivalent to 15% of their April and May premiums.

Loss and Loss Expenses

The increase in the loss and loss expense ratio in 2020, compared to 2019, was primarily the result of the following:

($ in millions) Favorable Prior Year Casualty Reserve Development

Details of the prior year casualty reserve development were as follows:

(Favorable)/Unfavorable Prior Year Casualty Reserve Development

General liability $ (35.0) (5.0) (9.5)

Businessowners' policies — — (3.0)

Total Standard Commercial Lines (85.0) (69.0) (58.0)

Homeowners — — 1.5

Personal automobile — 6.0 3.0

Total Standard Personal Lines — 6.0 4.5

Total (favorable) prior year casualty reserve development $ (85.0) (61.0) (41.5)

(Favorable) impact on loss ratio (3.2) pts (2.3) (1.7)

In addition to the prior year casualty reserve development, current year casualty loss costs were 1.7 points lower in 2020 compared to 2019, driven by decreases in frequencies reflecting reductions in miles driven due to the COVID-19-related governmental directives impacting our commercial and personal automobile lines of business.

For qualitative discussions regarding reserve development, refer to the insurance segment sections below.

Underwriting Expenses

Our underwriting expense ratio was 33.8% in 2020, which was flat compared to 2019. The expense ratio included 1.1 points of COVID-19 specific items, which included the $13.5 million addition to our allowance for credit losses on premiums receivable and lower net earned premiums from the audit premium accrual and premium credits. Excluding these COVID-19 specific items, our underlying expense ratio of 32.7% reflected our ongoing expense management initiatives, and about 70 basis points of temporary expense reductions mainly due to the lower travel, and entertainment expenses, and other expenses as a result of COVID-19.

Standard Commercial Lines Segment

Insurance Segments Results:

Less:

Combined Ratios:

Dividends to policyholders ratio 0.2 0.2 — 0.4 (0.2)

NPW growth in this segment in 2020 compared to 2019 reflected (i) renewal pure price increases, (ii) new business growth, and (iii) increased retention as shown below:

For the Year Ended December 31,

Renewal pure price increases on NPW 4.4 3.4

Consistent with our overall insurance operations, NPW growth in 2020 was negatively impacted by approximately 4 percentage points due to the following:

•Our $75 million estimate of audit and endorsement return premium related to the impact of COVID-19 on our workers compensation and general liability lines of business.

•A $15.4 million premium credit to our commercial automobile customers related to reduced miles driven and loss frequency due to the COVID-19 pandemic.

Consistent with the fluctuations in NPW, the increase in NPE in 2020 compared to 2019 reflected the items discussed above.

The 0.1-point increase in the loss and loss expense ratio in 2020 compared to 2019 was driven by the following:

($ in millions) Non-Catastrophe Property Losses Catastrophe Losses

In addition to the prior year casualty reserve development above, current year casualty loss costs were 1.2 points lower in 2020 compared to 2019, driven by decreased claim frequencies in our commercial automobile line of business reflecting reductions in miles driven due to the COVID-19-related governmental directives.

For quantitative information on the prior year development by line of business, see "Financial Highlights of Results for Years Ended December 2020, 2019, and 2018" above and for qualitative information about the significant drivers of this development, see the line of business discussions below.

The following is a discussion of our most significant Standard Commercial Lines of business:

General Liability

% of total standard commercial NPW 32 33 32

NPW in 2020 benefited from higher retention and renewal pure price increases. These items were partially offset by a $41.0 million reduction in audit and mid-term endorsement premiums, primarily driven by the COVID-19 pandemic, discussed in the "Insurance Operations" section above.

The combined ratio decreased 4.5 points in 2020, driven principally by an increase in favorable prior year casualty reserve development compared to 2019, asoutlined in the table below.

In 2020, the prior year reserve development was primarily attributable to favorable reserve development on loss severities in accident years 2017 and prior.

While this line experienced favorable prior year casualty reserve development in 2020, we remain cautious about the inherent uncertainty presented by COVID-19, including the potential for late reported claims and higher severities. Additionally, this line is exposed to other unfavorable trends, including social inflation and state laws enacted that extend the statute of limitations or open windows for previously time-barred actions. We will continue to monitor these trends in 2021.

Commercial Automobile

% of total standard commercial NPW 30 28 26

The increases in NPW shown in the table above reflect 8.1% renewal pure price increases, higher retention, and an increase in new business as in-force vehicle counts increased 7%. The increase in 2020 was partially offset by a $15.4 million premium credit to our commercial automobile customers as a result of the COVID-19 pandemic.

The 7.4-point decrease in the combined ratio in 2020 compared to 2019 was primarily driven by the items in the tables below.

($ in millions) Non-Catastrophe Property Losses Catastrophe Losses

The 2020 prior year casualty reserve development was primarily attributable to unfavorable reserve development on loss severities in accident years 2016 through 2019 and higher than expected frequencies in accident year 2019.

The lower combined ratio in 2020 also reflected a 6.7-point reduction in the current year casualty loss costs. This reduction primarily relates to the impact of strong renewal pure price increases we have earned in this line of business over the last several years and underwriting actions we have taken to improve profitability. Current year loss costs also benefited from decreases in claim frequencies reflecting reduced miles driven related to the COVID-19-related governmental directive.

This line of business remains an area of focus for us and most of the industry. Profitability challenges continue to generate

combined ratios higher than our risk-adjusted targets and the inherent uncertainty COVID-19 presents includes the potential for late reported claims and higher severities. We will continue to (i) actively implement price increases consistent with levels experienced in 2020, and (ii) enhance our underwriting tools to improve the accuracy of our rating information to prevent premium leakage. We also have been actively managing our new and renewal business, and we expect our actions will positively impact profitability through business mix improvement.

Workers Compensation

Retention 84 % 84 — pts 84 % — pts

Renewal pure price decreases (2.0) (2.8) 0.8 (0.2) (2.6)

% of total standard commercial NPW 12 14 16

In addition to the drivers in the table above, the 2020 NPW was impacted by a $28.7 million reduction in audit and mid-term endorsement premiums driven by the COVID-19 pandemic, which is discussed in the "Insurance Operations" section above.

The increase in the combined ratio in 2020 compared to 2019 was primarily driven by less favorable prior year casualty reserve development, as follows:

($ in millions)

The favorable reserve development for both periods was due to continued favorable medical severity trends impacting accident years 2018 and prior. Due to the length of time that injured workers can receive medical treatment, decreases in medical inflation can cause favorable loss development across an extended number of accident years.

While reported profitability on this line remains strong due to favorable emergence on prior year reserves, current accident year

margins do not support the continued negative pricing levels being set by the National Council on Compensation

Insurance and independent state rating bureaus. A reduction or reversal in the trend of favorable frequencies and severities has

the potential to significantly increase this line's combined ratio, which we monitor closely.

Commercial Property

% of total standard commercial NPW 19 17 17

NPW growth in this line in 2020 compared to 2019 was driven by (i) renewal pure price increases, (ii) new business growth, and (iii) increased retention.

Quantitative information regarding property losses is as follows:

Higher catastrophe losses in 2020 compared to 2019 were driven by the events mentioned in "Financial Highlights of Results for Years Ended December 31, 2020, 2019, and 2018" discussion above.

Standard Personal Lines Segment

Insurance Segments Results:

Less:

Combined Ratios:

NPW declined in 2020 compared to 2019, driven by new business that did not increase enough to compensate for the non-renewed policies reflected in our 83% retention ratio. Additionally, 2020 included a $4.3 million premium credit to our Standard Personal Lines customers as a result of the COVID-19 pandemic, which reduced the year-over-year NPW growth rate by 1 percentage point.

Renewal pure price increases on NPW 2.5 5.0

Direct new business premiums $ 44.7 40.7

The reduction in NPE in 2020 compared to 2019 reflects the decreases in NPW discussed above.

The loss and loss expense ratio increased 9.4 points in 2020 compared to 2019, the primary drivers of which were as follows:

($ in millions) Non-Catastrophe Property Losses Catastrophe Losses

($ in millions)

In addition to the items above, current year casualty loss costs were 2.6 points lower in 2020 as compared to 2019 driven by our personal automobile line of business reflecting decreases in claim frequencies as a result of reductions in miles driven due to the COVID-19-related governmental directives.

E&S Lines Segment

Insurance Segments Results:

Less:

Combined Ratios:

NPW increased 4.0% in 2020 due to increases in direct new business and renewal pure price. After two consecutive years in which we exited underperforming classes of business, our focus has shifted to profitably growing segments of our E&S book that have demonstrated underwriting profitability, and identifying new profitable segments to grow.

Quantitative information is as follows:

Overall renewal price increases 6.2 % 6.0

Direct new business premiums $ 113.9 96.8

The 2.0-point increase in the loss and loss expense ratio in 2020 compared to 2019 was primarily attributable to an increase in property losses. This was partially offset by lower unfavorable prior year casualty reserve development and a decrease in current year loss costs of 3.7 points.

Quantitative information regarding our property losses and prior year casualty reserve development are as follows:

($ in millions) Non-Catastrophe Property Losses Catastrophe Losses

We had no prior year casualty reserve development in 2020, which was a slight improvement over 2019, when unfavorable prior year casualty reserve development was relatively minor.

The 2.0-point increase in the underwriting expense ratio in 2020 compared to 2019 was primarily driven by increases in the bad debt provision during 2020 of 1.5 points.

Reinsurance

We use reinsurance to protect our capital resources and insure against losses on property and casualty risks that we underwrite. We use two main reinsurance vehicles: (i) a reinsurance pooling agreement among our Insurance Subsidiaries through which each company agrees to share in premiums and losses based on certain specified percentages; and (ii) reinsurance contracts and arrangements with third parties that cover various policies that we issue to our customers.

Reinsurance Pooling Agreement

The primary purposes of the reinsurance pooling agreement among our Insurance Subsidiaries are to:

•Pool or share proportionately the underwriting profit and loss results of property and casualty insurance underwriting operations through reinsurance;

•Reduce administration expenses; and

•Permit all of the Insurance Subsidiaries to obtain a uniform rating from AM Best Company ("AM Best").

The following illustrates the pooling percentages by Insurance Subsidiary as of December 31, 2020:

Insurance Subsidiary Pooling Percentage

Selective Insurance Company of America ("SICA") 32.0%

Selective Way Insurance Company ("SWIC") 21.0%

Selective Insurance Company of South Carolina ("SICSC") 9.0%

Selective Insurance Company of the Southeast ("SICSE") 7.0%

Selective Insurance Company of New York ("SICNY") 7.0%

Selective Casualty Insurance Company ("SCIC") 7.0%

Selective Auto Insurance Company of New Jersey ("SAICNJ") 6.0%

Mesa Underwriters Specialty Insurance Company ("MUSIC") 5.0%

Selective Insurance Company of New England ("SICNE") 3.0%

Selective Fire and Casualty Insurance Company ("SFCIC") 3.0%

Reinsurance Treaties and Arrangements

By entering into reinsurance treaties and arrangements, we can increase our underwriting capacity, accepting larger individual risks and aggregations of risks without directly increasing our capital or surplus. Our reinsurance program principally consists of traditional reinsurance. Under our reinsurance treaties, the reinsurer generally assumes a portion of the losses we cede to them in exchange for a portion of the premium. Amounts not reinsured below a specified dollar threshold are known as retention. Reinsurance does not legally discharge us from liability under the terms and limits of our policies, but it does make our reinsurer liable to us for the amount of liability we cede to them. Our reinsurers often rely on their own reinsurance programs, or retrocessions, to manage their large loss exposures. The size of the global reinsurance community is relatively small. If our reinsurers are unable to collect on their retrocessional programs, it may impair their ability to pay us for the amounts we cede to them.

Consequently, our reinsurers present us with direct and indirect counterparty credit risk. We attempt to mitigate this credit risk by (i) pursuing relationships with reinsurers rated “A-” or higher by AM Best and/or (ii) obtaining collateral to secure reinsurance obligations. Some of our reinsurance treaties permit us to terminate or commute them — or require the reinsurer to post collateral if the reinsurer's financial condition or rating deteriorates. We monitor our reinsurers' financial condition, and we review the quality of reinsurance recoverables and reserves for uncollectible reinsurance. For additional information regarding our reinsurance counterparty credit risk, see Note 9. "Reinsurance" in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K.

We have reinsurance contracts that separately cover our property and casualty insurance business that can be segregated into the following key categories:

•Property Reinsurance, which includes our (i) property excess of loss treaties purchased for protection against large individual property losses and (ii) property catastrophe treaties purchased to provide protection for the overall property portfolio against severe catastrophic events. We primarily use facultative reinsurance for large individual property risks greater than our property excess of loss treaty capacity.

•Casualty Reinsurance, which provides protection for both individual large casualty losses and catastrophic casualty losses involving multiple claimants or insureds. We also may use facultative reinsurance for large individual casualty risks in excess of our treaty capacity.

•Terrorism Reinsurance, which provides a federal reinsurance backstop, behind the protection built into our property and casualty reinsurance treaties, for terrorism losses covered under the Terrorism Risk Insurance Program Reauthorization Act (“TRIPRA”). For further information about TRIPRA, see Item 1A. “Risk Factors.” of this Form 10-K.

•Flood Reinsurance, for which all of the premiums and losses related to our participation in the WYO (for which we also receive a servicing fee) are 100% ceded to the federal government.

Property Reinsurance

We renewed the property catastrophe treaty, which covers both our standard market and E&S business, effective January 1, 2021. For the main property catastrophe excess of loss treaty program, we maintained our expiring retention. We also purchased an additional $50 million in limit at the top of our program, thereby extending the coverage to $785 million in excess of a $40 million retention.We also renewed the separate catastrophe treaty of $35 million in excess of $5 million that covers events outside our 2015 22-state footprint and supports (i) our standard lines geographic expansion into Arizona, New Hampshire, Colorado, Utah, and New Mexico and (ii) our growing E&S property book. Both treaties were renewed on substantially the same terms as the expiring treaties except (i) restrictions in coverage were imposed related to the systemic perils of communicable disease and (ii) first party cybersecurity coverage, an expected result consistent with current market conditions. Consequently, the property catastrophe program now excludes coverage for communicable disease, but it retains reduced reinsurance coverage for cybersecurity risks. Despite these new limitations, coverage for traditionally covered property perils was maintained. Overall catastrophe ceded premium for 2021 increased due to three factors: (i) increases in underlying property exposures in line with our growing overall portfolio; (ii) the new additional $50 million of coverage purchased at the top of our treaty to maintain stability in our net risk profile; and (iii) a reinsurance environment characterized by higher risk-adjusted pricing, more rigorous underwriting, and reduced capacity. These dynamics were fueled by such factors as the uncertainty surrounding the impact of COVID-19, lower interest rates, and elevated catastrophe loss activity. However, on a risk-adjusted basis, the expiring layers saw modest rate increases, in line with market conditions for loss-free accounts sharing our geographic footprint.

We seek to minimize credit risk within our reinsurance program by transacting with highly-rated reinsurance partners and, where feasible, purchasing collateralized reinsurance products, particularly for high-severity, low-probability events. The current reinsurance program includes $281 million in collateralized limit, primarily in the top layer of the catastrophe program.

We continue to assess our property catastrophe exposure aggregations, modeled results, and effects of premium growth on our property portfolio. We strive to balance our exposure to individual large events against the cost of reinsurance protections.

We model various catastrophic perils, and hurricane risk continues to be our portfolio's most significant natural catastrophe peril because of the geographic location of the risks we insure. The table below illustrates the impact of the five largest hurricane losses we have experienced in the last 30 years:

($ in millions) Actual Gross Loss Net Loss2 AccidentYear

Hurricane Name

1This amount represents reported and unreported gross losses estimated as of December 31, 2020.

2Net loss does not include reinstatement premiums, taxes, or flood claims handling fees.

We review our exposure to hurricane risk by examining the results of a third-party vendor model and proprietary analysis. The third-party vendor model provides a long-term view that closely relates modeled event frequency to historical hurricane activity and is adjusted to reflect assumptions for certain non-modeled costs, such as the impact of loss expenses, residual market assessments, and automobile-related losses. We believe that modeled estimates provide a range of potential outcomes, and we review multiple estimates to understand our catastrophic risk.

Occurrence Exceedence Probability Modeled Losses

1Gross losses include uncertainty associated with damage/loss estimation, demand and storm surge, and assumptions for certain un-modeled costs, such as the impact of loss expenses, residual market assessments, and automobile-related losses, which collectively increase our gross losses by approximately 13%.

2Net losses are after-tax losses net of catastrophe reinsurance including reinstatement premiums.

SIGI US Equity

SIGI · 10-K · period ended 2020-12-31

Item 1A. Risk Factors.

Item 1B. Unresolved Staff Comments.

Item 2. Properties.

Item 3. Legal Proceedings.

Item 5. Market For Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities.

Item 6. Selected Financial Data.

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations.

SIGI US Equity☆

SIGI · 10-K · period ended 2020-12-31

Item 1A. Risk Factors.

Item 1B. Unresolved Staff Comments.

Item 2. Properties.

Item 3. Legal Proceedings.

Item 5. Market For Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities.

Item 6. Selected Financial Data.

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations.

SIGI US Equity