Sex on a spectrum in the binary world of sport: the CAS’s decision in the case of Caster Semenya & Ors v the IAAF

Published 08 May 2019 By: Celia Rooney

Athletics Track

On 30 April 2019, the Court of Arbitration for Sport (CAS) delivered its award in the case of Caster Semenya & Athletics South Africa v the International Association of Athletics Federation, dismissing Ms Semenya’s request for arbitration and upholding the validity of the IAAF Regulations for Female Classification (Athletes with Differences of Sex Development) (the DSD Regulations).

In one of the most controversial sporting disputes in recent years, Ms Semenya sought to challenge the DSD Regulations, which place restrictions on the eligibility of women to compete as women in certain sporting events. The finding against her means that, unless she takes measures to reduce her endogenous testosterone levels, she will be unable to compete in events between 400 meters and one mile at the international level.

While the CAS’s full award is yet to be published, the reasons offered for the decision to date make for an interesting read and are considered below. The Executive Summary and Press Release are available here and here, respectively.

Who is Caster Semenya?

Caster Semenya is a 28-year old South African middle-distance runner. These days a household name, Ms Semenya burst onto the stage of international athletics in 2009, winning gold in the 800m at the World Championships in Berlin.

Ms Semenya’s success was quickly tarnished by allegations that she was not a woman and that she was undergoing tests to confirm her sex. While the results of those tests have never been made public, it is understood that Ms Semenya has a difference of sex development (DSD) which, as explained further below, means that while she is female, her sexual development has been atypical.

Following the controversy in Berlin, Caster Semenya was subsequently withdrawn from international competition until 6 July 2010 when, it is understood that following hormone treatment, she was allowed to return to international athletics. Ms Semenya went on to compete successfully in a number of international events, winning silver medals in the 800m at both the World Championships in South Korea in 2011 and the London Olympics in 2012 (both of which were bumped up to gold, following the disqualification of the winning Russian athlete for doping offences). For the reasons set out below, Ms Semenya was also able to compete without any hormone treatment between July 2015 and April 2018, during which time she won the gold medal for the 800m at the Olympic Games in Rio de Janeiro, Brazil.

What is a DSD? What is hyperandrogenism?

In cases of typical sexual development, an individual will have XX chromosomes if she is female and XY chromosomes if he is male. Where a Y chromosome is present, a baby will ordinarily develop testes around the tenth week of pregnancy. Absent any Y chromosome, a baby will ordinarily develop ovaries.

Disorders of sex development”, or DSDs, are a group of rare conditions, characterised by atypical sexual development. There are many different types of DSD. Some individuals with a DSD, for example, will have XX chromosomes but “ambiguous” or male-looking genitalia, or will be born without a womb. Others may have neither a second X chromosome nor a Y chromosome (XO), or will have an additional chromosome (XXY), which will typically result in atypical development during puberty.

A further type of DSD exists where women have female external genitalia, XY chromosomes and undescended testes. This particular DSD is referred to by doctors as “46 XY” (the majority of the DSDs that are the subject of the DSD Regulations, as set out further below).

Athletes with a DSD will typically have hyperandrogenism, meaning that they will have naturally elevated levels of androgens, including testosterone. An athlete may have high levels of testosterone without the hormone having any effect (or any notable effect) on her body because, for example, she is insensitive or resistant to androgens.

Binary categories: distinguishing sex for sporting purposes

Elite male athletes outperform elite female athletes by an estimated 10% in sports that rely on endurance and strength. In recognition of that competitive advantage, since 1928, athletics competitions have been strictly divided into male and female classifications.

Those binary categories, however, are deceptively simple and the eligibility criteria and the means of their application have long been a source of controversy in sport. Before the development of molecular medicine, for example, all female athletes – with the exception, rumour has it, of Princess Anne - were subjected to a compulsory physical examination to verify their sex. Thereafter, while scientific developments enabled sports governing bodies to test for X and Y chromosomes and even for specific genes on those chromosomes, there was still considerable room for error (arising, for example, from genetic mutations).

In April 2011, the IAAF enacted its Regulations Governing Eligibility of Females with Hyperandrogenism to Compete in Women’s Competition (the Hyperandrogenism Regulations). The enactment of the Hyperandrogenism Regulations represented a major shift in sex verification for sporting purposes in that, for the first time, an international sports governing body was focusing primarily on testosterone, instead of genetics, to determine sex.

In 2014, a 19-year old Indian athlete, Dutee Chand, appealed to CAS, challenging her indefinite ban for elevated testosterone levels under the IAAF’s Hyperandrogenism Regulations. The CAS cleared Ms Chand to compete1, suspending the Hyperandrogenism Regulations for two years.

In that case:

  • it was not in dispute that the Hyperandrogenism Regulations were discriminatory, since only female athletes were required to undergo testing for endogenous testosterone and the regulations placed restrictions on the eligibility of athletes on the basis of certain natural physical characteristics;

  • on the balance of probabilities, the CAS concluded that there is a scientific basis for using testosterone as a marker for the purposes of the Hyperandrogenism Regulations, finding that testosterone was a key biological indicator of the difference between male and female athletes; however,

  • while the CAS recognised that the over-representation of DSD females in elite sport constituted indirect evidence that high levels of endogenous testosterone improved athletic performance, there was insufficient evidence about the degree of the advantage that androgen-sensitive hyperandrogenic females (i.e. female athletes who not only had high levels of testosterone but were also able to use that testosterone) had over other female athletes. In the absence of such evidence, the CAS could not conclude that the Hyperandrogenism Regulations were necessary, reasonable and proportionate. The CAS therefore suspended the regulations during which time the IAAF was permitted to submit further written evidence of the performance advantage arising from testosterone.

The DSD Regulations

In March 2018, the IAAF informed the CAS that it intended to withdraw and replace the Hyperandrogenism Regulations. The following month, the IAAF enacted the DSD Regulations.

The DSD Regulations establish new requirements governing the eligibility of women with certain DSDs to participate in the female classification in eight events (the Restricted Events). The Restricted Events include the 400m, 800m and 1500m races (Regulation 2.2(b)2). Caster Semenya regularly participates in each of those events at the international level.

DSD athletes with XX chromosomes do not fall within the scope of the new regulations, in their amended form. Instead, a female athlete will only fall within the scope of the DSD Regulations where she has: one of a number of specific DSDs (which, in the new regulations (as amended) involve XY chromosomes only); an endogenous testosterone level of 5 nmol/L or above; and “sufficient androgen sensitivity for those levels of testosterone to have a material androgenising effect” (Regulation 2.2(a)). Athletes with 46 XY DSD ordinarily have testosterone levels well into the male range.

An athlete that falls within the scope of the DSD Regulations will only be able to compete in a Restricted Event on the international stage where she:

  • is recognised at law as female or intersex or an equivalent;

  • reduces her blood testosterone to below 5 nmol/L for a continuous period of at least 6 months by, for example, using hormonal contraceptives; and

  • maintains that level of testosterone both in and out of competition.

There is strict liability for compliance with the eligibility requirements (Regulation 3.14), which is the sole responsibility of the affected athlete (Regulation 3.11).

The DSD Regulations expressly note that the eligibility requirements do not prohibit an athlete from competing in non-international competitions or in anything other than the Restricted Events (Regulation 2.6). The regulations also seek to reassure affected athletes that “surgical anatomical changes are not required” (Regulation 2.4) and that they are permitted to compete in the male classification or any intersex competition (Regulation 2.6(b) and (c)).

The stated purpose of the DSD Regulations is to ensure “fair and meaningful competition in the sport of athletics”, by making sure that competition is organised “within categories that create a level playing field”. The Regulations are premised upon the idea that “high levels of endogenous testosterone circulating in athletes with certain DSDs can significantly enhance their sporting performance”, a proposition for which there is said to be a “broad medical and scientific consensus” (Regulation 1.1(d)).

The Challenge

The DSD Regulations were due to come into force on 1 November 2018. Before that date, Caster Semenya and Athletics South Africa commenced arbitral proceedings before the CAS challenging the validity of the regulations, seeking declarations that they were invalid and void. The implementation of the DSD Regulations was delayed pending the challenge.

The precise way in which Ms Semenya articulated her grounds of challenge will remain unclear unless and until further details of the CAS’s award are published. In summary, however, it is understood that the position of Ms Semenya and Athletics South Africa was that the DSD Regulations:

  • unfairly discriminate against athletes on the basis of sex and/or gender because they only apply to female athletes and to female athletes having certain physiological traits;

  • lack a sound scientific basis;

  • are not necessary to ensure fair competition within the female classification; and

  • are likely to cause grave, unjustified and irreparable harm to affected female athletes.

On that basis, Ms Semenya and Athletics South Africa claimed that the Regulations are unfairly discriminatory, arbitrary and disproportionate and therefore violated the IAAF Constitution, the Olympic Charter, the laws of Monaco (where the IAAF has its headquarters), the law of the various jurisdictions in which international athletics competitions are held, and universally recognised fundamental human rights.

In response, the IAAF submitted that the DSD Regulations did not discriminate on the basis of a protected characteristic, were based on the best available scientific evidence, and were a necessary, reasonable and proportionate means of pursuing the legitimate aim of safeguarding fair competition and protecting the ability of female athletes to compete on a level playing field.

Decision of the CAS

By a majority, the CAS dismissed Ms Semenya’s requests for arbitration and confirmed the validity of the DSD Regulations.

The Panel unanimously concluded that the DSD Regulations are discriminatory, since they target a subset of female athletes (without imposing any restriction on their male counterparts) and since the regulations target a group of individuals on their immutable biological characteristics: see further, paragraphs 14 and 15 of the Executive Summary. That finding is unsurprising in light of the decision in Dutee Chand (where the issue was not even in dispute).

A majority of the Panel concluded that the IAAF had succeeded in establishing that the DSD Regulations were necessary: see further paragraphs 16 to 24 of the Executive Summary.

  • It was not in dispute that it was legitimate to have separate, binary categories in sports for men and women, which in turn required the IAAF to devise a means of determining which athletes fall into each category. The Panel in turn accepted the IAAF’s submission that categorisation on the basis of a person’s legal sex may not always constitute a fair and effective means of categorising athletes for the purpose of sport. The purpose of having separate categories for men and women was not to protect women from having to compete against men per se, but rather to protect those individuals who “lack insuperable performance advantages” from having to compete against those with such advantages. The fact that a person was recognised as a woman in law did not mean that she lacked those performance advantages.

  • The Panel unanimously found that found that endogenous testosterone is the primary driver of sex difference in sports performance between men and women. The CAS agreed with the IAAF that all of the factors that contributed to sporting performance are equally available to men and women, except exposure to adult male testosterone. Thus, if the male-female divide in sport is really a divide between those with and without the testosterone-derived advantage, then it is necessarily “category defeating” to permit any individuals who possess the higher levels of testosterone to compete in the lower-testosterone category.

  • A majority of the panel concluded that elevated testosterone levels in athletes with 46 XY DSD gave such athletes a significant performance advantage over other female athletes. That conclusion – which is likely to be a source of controversy amongst experts in the field – was based on evidence concerning the performances and statistical over-representation of female athletes with 46 XY DSD,

Finally, a majority of the Panel concluded that the DSD Regulations constituted a proportionate interference with the rights of 46 XY DSD athletes: see further paragraphs 25 and 26 of the Executive Summary. The CAS appears to have reached that conclusion on the basis that the DSD Regulations do not require athletes to undergo surgical intervention, and instead rely on athletes taking oral contraceptives. The CAS nonetheless expressed concerns as to how the DSD Regulations would operate in practice. In particular, the CAS voiced its concerns:

  • about the side effects of hormonal treatment;

  • that while the DSD Regulations imposed strict liability on athletes, athletes may inadvertently be unable consistently to maintain a natural testosterone level below 5 nmol/L; and

  • that there was a lack of concrete evidence of actual significant athletic advantage by a sufficient number of 46 XY DSD athletes in both the 1500m and 1 mile events, and the IAAF was cautioned against applying the regulations to those events until further evidence is available. The IAAF has confirmed that it will continue to include the 1500m as a Restricted Event.


Caster Semenya’s athletic achievements have been the source of controversy for nearly a decade. Her CAS case has been no less charged. On being informed of the decision, for example, Athletics South Africa went as far as to say that, by allowing the IAAF to justify the discrimination in this case, the CAS had “seen fit to open the wounds of apartheid”.3

As the CAS recognised, the “imperfect alignment of nature, law and identity” is what gives rise to the conundrum in Caster Semenya’s case. The CAS was in the invidious position of having to reconcile the existence of the binary male/female athletics system (itself not in dispute in the case) with the biological reality that sex is not binary and instead exists on a spectrum. The controversy generated by this case is further exacerbated by the conflation of issues of sex and gender – the former a matter of biology, the latter of sociology.

As noted above, the CAS was not invited to question the binary categorisation of athletes into male and female competitors. Its decision was nonetheless inextricable from its conclusion that “the male-female divide in competitive athletics is not to protect athletes with a female legal sex from having to compete against athletes with a male legal sex”, nor to protect athletes with a female gender identity from having to compete against those with a male gender identity, but is rather to protect those without certain “insuperable performance advantages” from having to compete against those with those advantages. There may well be logic in that criterion, but it is unsurprising that its application to distinguish athletes into two camps – male and female, with outliers that fall into neither group – generates controversy and stigma.

It is difficult to assess the legal or evidential merits of the CAS Panel’s position, in circumstances where the full award with reasons has not yet been published. The entire decision pivots on the CAS Panel’s finding, as a matter of medical evidence, that high levels of endogenous testosterone necessarily give 46 XY DSD athletes a significant performance advantage over other female athletes. There have always been scientists who question the simplicity of that conclusion pointing to, amongst other things, the importance of an athlete’s sensitivity to such androgens and (as the CAS Panel itself recognised in respect of the longer races) the lack of available evidence. The merits of the CAS judgment therefore are likely to be best assessed by the medical community, upon further disclosure of the Panel’s reasons.

Ultimately, there are no simple answers to the Caster Semenya saga, or the issues arising from the inclusion of DSD athletes in elite sport. It may be that scientific evidence supports the conclusion that eligibility requirements for DSD athletes are a necessary evil to ensure fair competition in female sport. That said, there are good reasons to approach the DSD Regulations with caution. As the Panel itself recognised, there is a paucity of evidence of performance advantage – particularly in respect of certain events. Moreover, there are good historical and ethical reasons to raise an eyebrow in respect of any law that requires women to artificially alter their naturally occurring hormones so as to enter their preferred profession.4 In this respect, the fact that the regulations do not mandate surgical intervention will be of little consolation to the athletes affected by the DSD Regulations, nor can it possibly be indicative of their proportionality.

Caster Semenya – like other DSD athletes before her – has found herself at the heart of one of the most difficult and controversial issues in sport. The Panel was right to recognise the “grace and fortitude” with which she has conducted herself for the last decade, and that she has done nothing wrong. When bringing her CAS case, Caster Semenya made one simple public statement: “I am Mokgadi Caster Semenya. I am a woman and I am fast”. Whatever the complexities of this case, that much is not in dispute. 

This article was first published on Blackstone Chambers Sports Law Bulletin. The original is available to view here.

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Celia Rooney

Celia Rooney

Barrister, Blackstone Chambers

Celia practises across all of Chambers’ main areas of work, with particular experience of commercial disputes, sports law, public law and human rights, and employment. She is frequently instructed in cases where there is significant degree of overlap between her specialisms, such as commercial judicial reviews and sports and employment cases involving allegations of fraud. Similarly, from October to December 2016, Celia acted as sole legal counsel for the Payment Systems Regulator, advising on a 'super-complaint' by the consumer group, Which?, concerning authorised push payment fraud.

She has experience before a range of tribunals, including the High Court, Court of Appeal and Supreme Court  and has also appeared in cases before a number of regulatory bodies, such as The FA Regulatory Commission and Appeal Board.