Mokgadi Caster Semenya & Athletics South Africa v. IAAF

Background

In April 2018, the IAAF (now World Athletics) introduced its Eligibility Regulations for the Female Classification (Athletes with Differences of Sex Development) — the DSD Regulations. They applied to female athletes with 46,XY DSD who had a natural testosterone level above 5 nmol/L and who experienced what the IAAF termed a material androgenising effect. Affected athletes wishing to compete internationally in restricted events from 400m to the mile were required to medically suppress their testosterone below that threshold and maintain it for at least six months beforehand.

Mokgadi Caster Semenya, a multiple Olympic and World champion over 800m, filed a request for arbitration against the IAAF on 18 June 2018; Athletics South Africa (ASA), her national federation, filed a parallel request. Both sought a declaration that the DSD Regulations were unlawful and an order preventing their entry into force. The Panel — the Hon. Annabelle Bennett AO SC (President), the Hon. Hugh Fraser, and Dr Hans Nater — heard the matter over five days in February 2019 and issued its award on 30 April 2019.

Issues Before the Panel

• Whether the DSD Regulations were discriminatory against the Claimants on the grounds of sex, gender identity, and/or innate physical characteristics.
• If discriminatory, whether that discrimination was nonetheless a necessary, reasonable, and proportionate means of achieving a legitimate sporting objective — namely, fair and meaningful competition in the female category.
• Whether the specific mechanics of the Regulations — the intimate physical examinations used to assess virilisation, and the requirement to maintain testosterone continuously below 5 nmol/L — were themselves proportionate, given the practical difficulty of compliance.

The Claimants' Case

Semenya and ASA argued that the Regulations unfairly singled out a group of women for differential treatment based on an innate biological trait, without a sufficiently robust scientific basis linking endogenous testosterone specifically to a performance advantage in the restricted events. They contended the Regulations were impossible to comply with consistently, given that an individual athlete's testosterone levels can fluctuate significantly rather than remaining fixed. They further argued that requiring an athlete to submit to hormonal suppression, or to an intimate physical examination, merely to continue competing as herself was a disproportionate intrusion, and that the Regulations were arbitrary, discriminatory, and contrary to the IAAF Constitution, the Olympic Charter, and Swiss public policy.

The IAAF's Response

The IAAF accepted that all sporting classification necessarily draws lines based on physical characteristics, and framed the real question as whether this particular line was justified. It adduced expert evidence that circulating testosterone is the principal driver of the male performance advantage, and statistical evidence that 46,XY DSD athletes with testosterone in the male range were significantly overrepresented among elite performers in the restricted events relative to their prevalence in the general population. It argued the Regulations were the least restrictive means available to protect the integrity of the female category without resorting to more invasive chromosomal or anatomical screening.

The Panel's Decision and Reasoning

By majority (2–1), the Panel dismissed both requests for arbitration. It found that the DSD Regulations were indeed discriminatory, but held that, on the evidence before it, the discrimination was a necessary, reasonable, and proportionate means of achieving the IAAF's legitimate aim of preserving fair competition for female athletes in the affected events. Significantly, the majority accepted that the IAAF did not need to establish its scientific justification to a standard of certainty — an honest and good-faith view, reasonably held on the available evidence, was sufficient to satisfy its burden.

Subsequent Proceedings: Swiss Courts and the European Court of Human Rights

Semenya did not stop at the CAS award. She appealed to the Swiss Federal Supreme Court (the sole avenue to challenge a CAS award under Swiss arbitration law), which dismissed her appeal on 25 August 2020, holding that CAS's proportionality analysis did not violate Swiss public policy. With her competitive options narrowing, she then lodged an application against Switzerland at the European Court of Human Rights in February 2021, arguing that the Federal Supreme Court's deferential review of the CAS award had denied her effective legal protection against discrimination.

In a Chamber judgment of 11 July 2023, the ECtHR found, by a narrow majority, a violation of Article 14 (prohibition of discrimination) taken together with Article 8 (right to respect for private life), and of Article 13 (right to an effective remedy) taken together with those provisions — holding that Switzerland's courts had failed to provide the institutional and procedural safeguards needed to properly examine Semenya's discrimination claims. Switzerland requested referral to the Grand Chamber, which agreed to rehear the case.

On 10 July 2025, the Grand Chamber reversed course. It held that it had no jurisdiction to examine Semenya's substantive complaints under Articles 8, 13, and 14 at all, reasoning that Switzerland lacked the necessary jurisdictional link to those claims: Semenya is a South African national, and World Athletics (the regulation-making body) is seated in Monaco, not Switzerland. Those complaints were accordingly declared inadmissible — a materially narrower jurisdictional theory than the Chamber had applied two years earlier. The Grand Chamber did, however, find a violation of Article 6 § 1 (the right to a fair hearing), on the basis of the Federal Supreme Court's very limited scope of review of CAS awards.

The practical effect is significant and easily misstated: the Grand Chamber's judgment does not revisit or overturn the substantive finding that the DSD Regulations are lawful and proportionate — that question was found to fall outside Switzerland's Convention responsibility altogether. The surviving violation is procedural only, going to the adequacy of Swiss judicial review of arbitral awards generally, a point of considerable significance for CAS's institutional relationship with the Swiss courts, but one that leaves the DSD Regulations themselves, and Semenya's ineligibility to compete in the Restricted Events without testosterone suppression, undisturbed.

One member of the Panel dissented from the majority's conclusion, reflecting the genuinely contested nature of the evidentiary and proportionality questions at the heart of the case.

The Article 6 Standard the Grand Chamber Articulated

On the surviving Article 6 finding, the Grand Chamber set out a specific standard for how domestic courts must review CAS awards: because recourse to CAS arbitration is compulsory for elite athletes wishing to compete (they cannot decline it and still pursue their sport professionally) and because fundamental civil rights were genuinely at stake, the Swiss Federal Tribunal was required to conduct what the Court called a "particularly rigorous" examination of Semenya's challenge — engaging properly with the submissions, arguments, and evidence she raised, and giving specific reasons for rejecting them, rather than applying its ordinary, deferential public-policy standard of review. The Court held Switzerland had not met that standard in 2020. This procedural holding carries significance well beyond Semenya's own case: it puts every state that hosts compulsory sports arbitration on notice that ordinary judicial deference to an arbitral award may not suffice where fundamental rights are genuinely in dispute, without in any way disturbing the substantive lawfulness of the DSD Regulations themselves, which the Grand Chamber never reached.