In 2012, then Vice President Joe Biden proclaimed discrimination against transgender individuals to be the “civil rights issue of our time.”Footnote 1 The Obama administration and, subsequently, the Biden administration took the position that discrimination against transgendered individuals was a prohibited form of sex discrimination and interpreted federal antidiscrimination statutes in accordance with this view. In 2020, the Supreme Court agreed, holding that in the employment context, where careers are open to talents, and men and women compete directly against each other for rewards, transgender individuals could not simply be excluded from the tournament.
Yet, for the Obama and Biden administrations, equality for transgender individuals required not only ending their exclusion from coed spaces but demanding their inclusion in sex-segregated spaces on the basis of gender identity. In the context of education, this meant requiring that schools generally permit transgender girls to participate on the sports teams – and use the bathrooms and locker rooms – associated with their gender identity, not their biological sex. It was this demand for transgender inclusion in sex segregated spaces, far more than the call for nondiscrimination in unisex contexts like employment, that proved controversial.
The issue of transgender women’s participation in women’s sports captured national attention in 2021 when Lia Thomas, a student-athlete at Penn, joined the women’s varsity swim team after previously swimming for two years on the men’s team. Thomas had taken female hormones for one year, making her eligible, at that time, to participate on the women’s team. Competing in the women’s category, Thomas had tremendous success – even winning an NCAA Division I national championship – far outshining her more modest results in the men’s category. Thomas’ success in the pool – and her presence in the women’s locker room – sparked widespread debate.
With Donald Trump’s election in 2024, the political pendulum shifted dramatically. On his first day in office, President Trump issued an executive order announcing that the state would recognize only two sexes defined in terms of biology at birth.Footnote 2 He followed this order just two weeks later with one specifically and categorically barring transgender girls and women from women’s sports in educational programs.Footnote 3
Although the political winds have changed, the debate is far from over and policy is far from settled. This book provides a critical examination of the legal, scientific and ethical issues raised by transgender girls’ inclusion in girls’ sports. It challenges the absolutist positions that have dominated the popular and political discourse and offers a more nuanced framework for deciding when transgender girls and women should, and should not, be permitted to compete in women’s sports.
While some of the analysis of this book will likely be useful in contexts other than sports, this book is, quite deliberately, narrow in scope. What is at stake when we think about transgender girls’ and women’s inclusion in female sports is different from what is at stake when we think about transgender women’s inclusion in sex-segregated bathrooms, prisons or locker rooms. As a result, the framework for fairly allocating the relevant goods and benefits in each context will differ, and so too will our likely answers to questions of inclusion. Transgender rights are, in other words, appropriately contextual.
In broad strokes, the book is divided into three parts. The first part explores the legal and scientific issues raised by transgender girls’ inclusion in girls’ sports and explains why neither positive law nor medical science provides a clear answer to how eligibility rules should be drawn. Chapter 1 describes the multilayered, complicated and, at times, contradictory legal landscape governing school sports. At the federal level is Title IX, which prohibits discrimination on the basis of sex in educational programs that receive federal funding. At the state level are statutes which increasingly exclude transgender girls from girls’ sports in the name of ensuring fair competition. Both are subject to the equal protection demands of the federal constitution. The chapter explains why antidiscrimination mandates are so indeterminate in sex-segregated contexts and why, as a result, whether and when transgender girls must be included in girls’ sports is still very much an open question. Chapter 2 describes the science of sex and explains why it too cannot determine eligibility rules for girls’ sports. There is, in fact, significant agreement among scientists and medical professionals about what determines sex and what factors matter most for athletic success. Nonetheless, eligibility rules are, and must be, fundamentally social choices. Only with social agreement about the meaning and purpose of women’s sports, can science help with category assignments.
The second part of the book identifies the commitments and convictions underlying and motivating arguments for inclusion and exclusion of transgender girls and highlights their weaknesses. This part focuses on the most absolutist arguments on both sides. These positions are not strawmen, they are instead the views that have dominated public discourse and defined political action.
On the left, groups like the American Civil Liberties Union (ACLU), the National Women’s Law Center and the National Organization for Women assert their unqualified support for transgender women’s inclusion in women’s sports. The ACLU proclaims unequivocally that “[t]rans girls are girls” and that trans girls have a right to participate on athletic teams consistent with their gender identity.Footnote 4 The National Women’s Law Center likewise “firmly support[s] the inclusion of women and girls who are transgender in all aspects of school – including sports, restrooms, and locker rooms – as a matter of both civil rights law and of human rights.”Footnote 5 The National Organization of Women explains that “‘[d]ebate’ about [t]rans [g]irls and [w]omen in [s]chool [s]ports [s]preads [t]ransphobia and [b]igotry.”Footnote 6 Doubters, those who question whether transgender women should be fully included in women’s spaces, have been condemned, often viciously. Even the socially powerful and otherwise politically progressive have been subject to withering attacks. The treatment of J.K. Rowling, author of the Harry Potter books, is particularly noteworthy. In a series of tweets and longer writings, Rowling expressed her belief in the importance of biological sex and of single-sex spaces for biological women. She received in response widespread condemnation from Hollywood, including from the young stars of her movies, online abuse and threats of violence.Footnote 7
On the right, categorical exclusion of transgender girls and women from women’s sports has become both a talking point and policy priority for the Republican Party. In addition to President Trump’s executive order barring transgender girls from girls’ sports, the Republican-controlled House of Representatives voted in January 2025 to amend Title IX to require transgender girls’ exclusion.Footnote 8 Passage in the Senate is far less certain. At the state level, as of early 2025, twenty-five states have passed exclusionary eligibility rules for girls sports.Footnote 9
Chapters 3 and 4 explain why both absolutist positions are a mistake. Arguments for blanket inclusion unpersuasively deny the existence and relevance of biological sex. They also place tremendous weight on the subjective pain experienced by transgender girls who are excluded from girls’ sports, while ignoring the subjective pain experienced by cisgender girls forced to compete against them. Arguments for exclusion, by contrast, focus on the perceived unfairness to individual cisgender girls of being denied victories they might otherwise win, yet the arguments fail to explain why ensuring victories for cisgender girls requires that all trans girls be excluded or, moreover, why winning should determine eligibility rules for girls’ sports at all ages and all levels. Arguments for both inclusion and exclusion rest too on controversial and often overlooked conceptions of human flourishing and personhood.
The third part of the book suggests a nuanced, empirically informed and pragmatic framework for determining eligibility lines for girls’ sports. Central to it is the belief that questions of transgender girls’ inclusion in girls’ sports should be answered by identifying the benefits and goods that come from athletic participation and then drawing eligibility rules with an eye to maximizing these benefits for transgender and cisgender girls and boys alike. I identify three primary benefits of sports – basic benefits, special benefits and group benefits. The basic benefits are the physical and psychological benefits that athletic participants get from athletic endeavors. The special benefits are the distinct set of goods – sometimes tangible sometimes not – that go to the small group of winners. The group benefits are the goods that organized sports confer on those who do not themselves play but who identify with the winners. Nonparticipants who identify socially with athletic winners receive benefits in the form of self-esteem, role-modeling and social status that comes from the celebration of female athletes and the recognition of women as strong autonomous agents.
Although the benefits of sport attach to all levels of play, they attach to different levels in different degrees. At the early childhood and recreational levels, the basic benefits predominate as both the reason and the reward for play. At more elite levels, the special and group benefits of sports become more pronounced. At each level of play, eligibility rules should be drawn so as to maximize the benefits of sports for girls and women – both transgender and cisgender – recognizing that under some circumstances the interests of the two groups will in fact diverge.
This book is more analysis than argument, more philosophical than political. Its goal is not to “win” an argument, but to deepen the conversation by speaking to a range of audiences. First and foremost, I hope this book will speak to those who are themselves or through their family members grappling directly with these issues as athletic participants. Second, I hope it will speak to policymakers who are shaping at the federal, state or organizational level, eligibility rules for women’s sports. Finally, I hope the book will speak to judges. Courts will ultimately have to decide what policies are consistent with statutory and constitutional requirements. In July 2025, the Supreme Court accepted cert in two cases challenging absolute and categorical bans on transgender girls’ participation in girls’ sports.Footnote 10 These cases are important though their result is likely to be narrow. Whether the Supreme Court holds that absolute exclusions of transgender girls from girls’ sports are impermissible or permissible, lower courts will continue to face challenges to a broad and diverse range of less restrictive laws and policies. Deciding these cases will require courts to assess and understand the social benefits of sports, the goals of sex segregation in this context and the impact of transgender girls’ inclusion at different levels and ages of play. These are precisely the questions of this book. The answers are genuinely hard and the stakes truly high. We all deserve a more thoughtful discussion.
