Lia Thomas v. World Aquatics

Transgender swimmer Lia Thomas filed for arbitration at CAS in September 2023, challenging World Aquatics' 2022 "Policy on Eligibility for the Men's and Women's Competition Categories" as invalid and unlawful, arguing it discriminated against her contrary to the Olympic Charter, the World Aquatics Constitution, and Swiss law, including the European Convention on Human Rights and the Convention on the Elimination of All Forms of Discrimination against Women. That policy permits transgender women to compete in the female category only if they did not experience male puberty, or suppressed it before age 12, and maintain testosterone below 2.5 nmol/L; it separately created an "open" category for transgender athletes generally. World Aquatics, for its part, described the policy publicly as having been "rigorously developed on the basis of advice from leading medical and legal experts, and in careful consultation with athletes." Thomas accepted that fair competition is a legitimate sporting objective and that some regulation of transgender participation is appropriate, but argued these specific provisions were not necessary, reasonable, or proportionate to that objective.

At World Aquatics' request, the CAS Panel agreed to decide the question of Thomas's standing as a threshold, bifurcated issue before reaching (or declining to reach) the substance. Thomas objected to that sequencing, but the Panel proceeded with it anyway. Three CAS arbitrators found that Thomas was not registered with World Aquatics and was not, at the time, even a member of USA Swimming in a category that would let her compete in "Elite Events" as the policy defines them — her NCAA title for the University of Pennsylvania had been won in competitions outside the World Aquatics system entirely. The Panel specifically rejected the idea that USA Swimming's own domestic rules could determine when World Aquatics' international policy applied, stating it was "not for USA Swimming to determine where and under what conditions the Policy and the Operation Requirement are triggered" — that trigger, the Panel held, is registration for a World Aquatics competition itself, which Thomas had never done. On that basis, the Panel concluded she was "not sufficiently affected by the rules" to have standing to challenge them.

The timing carried real practical weight: the ruling came just 11 days before the 23 June 2024 deadline for entries to the Paris Olympic Games, effectively ending any realistic path for Thomas to qualify that summer regardless of the policy's underlying merits.

CAS did not reach the substance of the eligibility question at all as a result. The case is worth noting precisely because of what it does not decide — unlike the Semenya case already central to this library, which reached and analysed the merits of an eligibility rule on a full evidentiary record, this matter was resolved entirely on standing, leaving World Aquatics' underlying eligibility criteria untested by CAS on this occasion. World Aquatics welcomed the ruling as "a major step forward" for protecting women's sport; Thomas called the decision "deeply disappointing" and said blanket bans on trans women were discriminatory. Reaction split sharply along the lines of the broader public debate: former collegiate swimmer Riley Gaines, a vocal critic of Thomas's participation in women's swimming, publicly celebrated the outcome, while the advocacy group Athlete Ally condemned it as a denial of Thomas's rights.