This article explores the definition of ‘sportswoman’ as put forward in the Caster Semenya case (2019) and the Dutee Chand case (2015) before the Court of Arbitration for Sport (CAS). It analyses the structural and discursive factors that made it possible for the CAS to endorse a definition that reduces sex and gender to a matter concerning testosterone. By relying on the concept of intersectionality and analytical sensibilities fromCritical Legal Studies, the article shows that framing the cases as amatter of scientific dispute, instead of as concerning human rights, significantly influenced theCAS decisions. Moreover, structural elements of international sports law, such as the lack of knowledge of human rights among CAS arbitrators and a history of institutionalising gendered and racialised body norms through sporting regulations, further aided the affirmation of the ‘testosterone rules’.