Mokgadi Caster Semenya & Athletics South Africa v. IAAF

Semenya and Athletics South Africa challenged the IAAF’s (now World Athletics) Eligibility Regulations for female classification, which required female athletes with certain differences of sex development to medically lower their testosterone levels to compete in restricted track events (400m to the mile).

A divided CAS panel (2-1) dismissed both requests for arbitration, finding the regulations discriminatory but holding that the discrimination was “a necessary, reasonable and proportionate means” of preserving fair competition in the affected events.

The case has continued through the Swiss Federal Tribunal and, in 2025, the European Court of Human Rights Grand Chamber — which found Switzerland had violated its procedural obligations in reviewing the award. It remains the leading authority on the limits of CAS deference to sporting-body eligibility rules, and on judicial review of CAS awards.