When an athlete faces a hearing before the Court of Arbitration for Sport, the outcome often hinges on one question: whose evidence does the panel find most credible? CAS is the world's highest tribunal for resolving sports disputes. Its panels are composed of skilled legal minds, but they are not experts in every field that comes before them. That gap between legal reasoning and specialized knowledge is where expert witness testimony becomes decisive.
Expert witnesses at CAS are qualified professionals who explain technical, scientific, or industry-specific evidence in terms a panel can evaluate and act upon. Depending on the nature of the dispute, they may address how a prohibited substance entered an athlete's system, whether a governing body followed its own rules and procedures, how a contract should be interpreted in the context of industry custom, or what standard of care applies in a particular sport. Their role is not to advocate for one side. It is to educate the decision-makers.
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What Expert Witnesses Do at the Court of Arbitration for Sport
An expert witness is a qualified professional who provides testimony based on specialized knowledge. The expert's job is not to argue a position. It is to give the panel the information it needs to reach a well-reasoned decision in an objective manner.
A credible expert witness takes evidence that would otherwise be difficult for non-specialists to assess and presents it in a way that is clear, reliable, and actionable for a CAS Panel made up of lawyers to understand.
Types of Expert Witnesses Commonly Used in CAS Proceedings
The range of experts who appear before CAS reflects the wide variety of disputes the tribunal handles. Some of the most frequently retained include the following.
- Pharmacologists and toxicologists. These experts analyze how substances enter and exit the body. In anti-doping cases, they are often called upon to explain whether a detected substance is consistent with intentional use or could have resulted from environmental exposure or a contaminated product. Their testimony directly supports arguments about No Fault or Negligence and No Significant Fault or Negligence under the World Anti-Doping Code.
- Laboratory scientists and accreditation experts. WADA-accredited laboratories must follow strict protocols when collecting, storing, and analyzing samples. An expert in laboratory science can identify whether the proper chain of custody was maintained or whether testing procedures deviated from required standards. Even a small procedural error can cast doubt on the reliability of a result.
- Medical doctors and specialists. Physicians appear in a range of CAS cases. In Therapeutic Use Exemption (TUE) disputes, a treating doctor may testify about the medical necessity of a prohibited substance. In eligibility cases involving hyperandrogenism or gender eligibility regulations, endocrinologists and other specialists may be called to address physiological criteria that directly affect an athlete's right to compete.
- Sports industry and contract experts. In disputes involving agent agreements, sponsorship contracts, or employment terms, professionals with direct experience in sports business can testify about market standards, customary practices, and whether the terms at issue reflect fair value. This type of testimony can be decisive when a panel must interpret ambiguous contract language in its proper commercial context.
- Forensic document analysts. In cases involving whereabouts failures, alleged tampering, or disputed records, document analysts may be called to verify whether records were properly maintained or whether inconsistencies in documentation support or undermine a party's account of events.
- Selection and eligibility experts. When an athlete challenges a national federation's decision to exclude them from a team or competition, experts familiar with selection criteria and governance standards can assess whether the process was applied fairly and consistently. Their testimony often addresses whether a governing body followed its own published rules.
Hot-Tubbing and How It Works at CAS
One of the more distinctive features of expert testimony at CAS is a procedure informally known as hot-tubbing. The term may sound unusual, but the concept is straightforward and increasingly common in international arbitration.
In a traditional hearing, each side presents its experts separately. One party calls its witness, the other side cross-examines, and the process repeats. Hot-tubbing—also called concurrent expert evidence—changes this format entirely. Both experts appear before the panel at the same time and are questioned together. Areas of agreement surface quickly. So do genuine points of disagreement. The panel gains a clearer, more immediate picture of what the evidence actually establishes and where the real dispute lies.
The procedure also tends to reduce the adversarial quality that expert testimony can take on when witnesses appear in isolation. Seated side by side, experts are less likely to function as advocates and more likely to engage in direct, substantive dialogue. This benefits the panel and, when your expert is well-prepared, benefits your case.
Hot-tubbing carries strategic implications. If your expert is more credible and better prepared than the opposing expert, the format creates a side-by-side comparison that works in your favor. If your expert struggles under real-time questioning, that contrast is equally visible. This is why selecting and thoroughly preparing the right expert is essential before any CAS hearing.
Not every panel will use hot-tubbing. The decision is typically made during the procedural phase. An experienced sports law attorney can assess whether the procedure serves your interests and advocate accordingly.
