2019
Semenya v. IAAF
The IAAF's 2018 Eligibility Regulations required certain female athletes with a 46 XY chromosome pattern and natural testosterone above 5 nmol/L to medically lower it to compete in events from 400 meters to the mile. Caster Semenya and Athletics South Africa challenged the regulations before the Court of Arbitration for Sport as discriminatory, unnecessary, unreliable, and disproportionate. A three-member panel found, 2-1, that the regulations were indeed discriminatory on their face -- and ruled for the IAAF anyway, holding that discrimination in sport is lawful if it is a necessary, reasonable, and proportionate means to a legitimate aim. Semenya declined to lower her testosterone and has not competed in her preferred events since.
Why it still matters
This is the case that set the operative legal test for eligibility rules in sport: not whether a rule discriminates, but whether the discrimination is proportionate to a legitimate aim. Every subsequent challenge to a federation's classification rules argues inside that framework.
The old rule
Before this case, World Athletics's DSD Regulations existed on paper but had never been tested by a neutral arbitral body. There was no binding precedent on whether a federation could impose testosterone-based eligibility criteria on individual athletes without that criteria itself constituting unlawful discrimination.
The legal hinge
Proportionality, not a bar on discrimination itself. The panel's 2-1 majority found the regulations discriminatory on their face, then asked a second question: is the discrimination necessary, reasonable, and proportionate to a legitimate competitive aim? Finding that testosterone is the primary driver of the average male-female performance gap, the panel held preserving a fair female category was that legitimate aim, and that the regulations were proportionately designed to serve it -- for the events they found the evidence strong enough to support.
What people believe
CAS ruled that Semenya's biology disqualified her from women's competition.
What actually happened
The panel did not rule on Semenya's eligibility as settled fact. It ruled that a regulation it had already found discriminatory could still be lawful if proportionate -- and even found the evidentiary basis for including the 1500m and one-mile events comparatively weak, suggesting the IAAF postpone enforcement there pending stronger evidence. The IAAF did not adopt that suggestion.
What it cost
Semenya declined to undergo hormone-suppression treatment and has not competed in her preferred 800m distance since the regulations took effect. She went on to pursue further appeals at the Swiss Federal Tribunal and the European Court of Human Rights in the years after this decision -- proceedings this entry does not cover.
Who captured it
World Athletics retained the regulatory framework it had written, for the events the panel found sufficiently evidenced. Other DSD athletes in the same events face the same restriction, and other sports federations gained a tested legal template -- proportionality review, not a blanket non-discrimination bar -- for writing their own eligibility rules.
If it had gone the other way
Had the panel ruled the other way, World Athletics would have had to design a different eligibility framework for the affected events, or abandon testosterone-based classification for them entirely. The case's most durable contribution isn't that specific outcome -- it's the test itself: proportionality review is what federations and challengers alike now argue inside, in nearly every eligibility dispute since.
Sources
Historical summaries prepared from published opinions and secondary sources. Commentary and analysis, not legal advice.