Defining “Sex” For Sports?: Legal Frameworks Under Title IX

In recent years, the legal definition of “sex” has become the subject of an integral debate in the athletics community. International federations are moving towards chromosome or gene-based screening, while states in the United States have adopted various rules on how “sex” affects sports’  participation. Now, the US Supreme Court is being asked to decide how Title IX constrains institutional efforts to regulate who may compete in women’s sports, with oral arguments for West Virginia v. B.P.J. (2025) and Little v. Hecox (2024) scheduled on January 13, 2026. West Virginia v. B.P.J asks whether state policies that ban transgender students from participating in girls’ school sports are consistent with Title IX and the 14th Amendment’s Equal Protection Clause. Little v. Hecox similarly asks whether athletes should be required to compete under their biological sex as opposed to their gender identity. 

Both cases ask the Supreme Court a categorical question: when physical performance is directly at issue, can Title IX accommodate a context-specific interpretation of “sex?” Combined with state precedent, Title IX and the Equal Protection Clause enable the development of a sport-specific, puberty-based interpretative framework to defining sex, which contrasts the biological rigidity of international rules and categorical rules adopted by some states. 

Title IX established a statutory baseline and interpretative method for adjudicating sex-based claims in education, but the Bostock v. Clayton County (2020) case has complicated how courts read the operative term “sex.” Title IX prohibits discrimination “on the basis of sex” in federally funded education programs, and courts interpret that text in the light of the statute’s remedial purpose to secure equal opportunity in education and athletics across gender. In turn, Bostock v. Clayton County concluded that it is discriminatory to fire an employee on the motivation of an individual’s sexual orientation or gender identity because those traits are inextricably tied to sex, which Title VII prohibits. Although Bostock keeps sexual orientation and gender identity distinct, discrimination related to either trait can still result in sex-based claims. Courts would therefore need to reconcile Bostock’s inclusive interpretative approach to gender identity with Title IX and the Equal Protection Clause when defining who can participate in sports. Some lower-court decisions also utilized an integrated approach. In Gloucester County School Board v. G.G. (2017), the Fourth Circuit court recognized that transgender students may be protected under sex-discrimination frameworks in school contexts. Based on Title IX, this protection for transgender students should confer to athletics as well. However, Clark v. Arizona Interscholastic Association (1989) provides nuance, stating that athletic sex segregation must still exist to ensure fairness based on “physiological differences.” Taken together, these cases lead to a standard that allows transgender athletes who do not have any physiological advantage to compete, while barring those who do. 

This standard would offer necessary clarification since many federal challenges to state bans have involved transgender girls who did not undergo endogenous puberty. Relative to these aforementioned physiological differences, the main scientific differentiator between male and female development is puberty as testosterone leads to significant physiological changes, such as increased height, bone structure, muscle mass, and cardiovascular strength. In Doe v. Horne (2024), the district court granted a preliminary injunction on this basis and concluded that the plaintiffs were likely to succeed on their equal protection and Title IX claims since transgender girls who receive puberty-blocking medication do not have an athletic advantage over girls. This ruling treats developmental history as a relevant factual characteristic without adopting any categorical definition of “sex.” Doe v. Horne is an example of how courts have already weighed puberty-related evidence when administering Title IX in the athletics context. A similar situation occurred relative to Hecox v. Little, where transgender student Lindsey Hecox was barred from running for Boise State’s women’s cross-country team due to Idaho’s Fairness in Women’s Sports Act (2020). The district court also granted a preliminary injunction and concluded that Idaho’s Act likely violated the Equal Protection Clause and was not substantially related to the asserted interests in sex equality. Both Doe and Hecox show that courts are willing to assess the scientific role of puberty when determining if a transgender student is allowed to participate. 

With the pending West Virginia and Hecox cases, the Supreme Court has the opportunity to create a new standard to ensure that states do not continue to violate Title IX and the Equal Protection Clause for transgender athletes. For gender classifications, the Supreme Court must use the intermediate scrutiny standard, as was established in Craig v. Boren (1976). The intermediate scrutiny standard requires federal and state governments to ensure the law is substantially related to achieving an important governmental objective when considering gender-based classification. This was then changed in United States v. Virginia (1996), which requires all gender-based classifications to be heard with “heightened scrutiny.” This means that the Supreme Court must demonstrate their actions serve an important governmental interest and the gender-based classification is substantially related to achieving that interest. Applied to athletic eligibility, depending on the Supreme Court’s decision, this suggests two possible routes. The federal courts could treat categorical bans as sex-based classifications that are substantially related to the important interests of preserving fair competition, or they could adopt a narrower sport-specific reading of “sex” as an interpretative matter under Title IX. Either pathway would require federal courts to scrutinize whether less restrictive measures on transgender athletes would achieve the asserted objective as laid out in Title IX and the Equal Protection Clause. 

The question of whether Title IX can accommodate a context-specific interpretation of “sex” has identifiable doctrinal answers. According to one plausible reading, the Supreme Court could adopt a sport-specific, puberty-based interpretive framework under Title IX. Further eligibility rules would thus be subject to judicial review and be more narrowly tailored. Alternatively, with another reading by the Supreme Court, federal courts could resolve disputes through the constitutional route, applying the “heightened scrutiny” standard to any sex-based classification and requiring state and local governments to demonstrate a valid relationship between any transgender bans and competitive interests of fair sports. Both routes require the courts to assess scientific evidence about puberty. If the Supreme Court concludes that categorical transgender bans are not substantially related to the asserted interest in competitive fairness, they could respond by articulating a more uniform federal interpretation of “sex” for athletic contexts. No matter what the Supreme Court decides, the upcoming rulings for both Hecox and West Virginia will undoubtedly establish a new precedent for transgender athletes moving forward.