«Evidence in sports disputes: common issues and best practices before the CAS»

Legal framework: swiss law as a foundation

A key point Ariadna emphasized is that when parties submit a case to the CAS, they are not only choosing an arbitration forum—they are also accepting that Swiss law governs the procedure. Specifically, Chapter 12 of the Swiss Private International Law Act applies. According to Ariadna, this legal foundation is more rigid and technical than the typically more flexible and evolving norms found in sports regulations such as those from FIFA.

Admissible types of evidence

Unlike proceedings before FIFA, where only written evidence is typically allowed, CAS accepts a wider range of evidentiary materials. Ariadna outlined the following types:

• Written documents, such as contracts, statutes, powers of attorney, and official correspondence.
• Witness testimony, to contextualize and expand on written records.
• Expert reports, especially in technical or medical areas.
• Evidentiary requests to the panel, such as asking the tribunal to compel the other party to produce a document under their control.

As Ariadna pointed out, “A document alone rarely tells the whole story.” Supporting it with testimony or expert insight helps build a stronger narrative.

Strategic use of evidentiary measures

One powerful procedural tool discussed by Ariadna is the ability to request the CAS panel to order the other party to disclose documents or evidence that may support your case. This mechanism, similar to “discovery” in common law systems, is not commonly used in civil law jurisdictions but is permitted under the CAS Code.

Importantly, the requesting party must prove the document exists and is relevant, and cannot simply speculate. Ariadna encouraged lawyers to be specific and well-prepared when invoking this right.

Burden of proof: general rules and exceptions

Ariadna explained that the general principle is straightforward: the party making a claim must prove it. However, sports law introduces several exceptions, especially in disciplinary and anti-doping cases.

In FIFA disciplinary proceedings, it is FIFA’s responsibility to prove the infraction, not the accused party’s job to disprove it. In anti-doping matters, while the organization must show a rule violation occurred—often through a positive test—the burden then shifts to the athlete to prove mitigating factors, such as the absence of intent or the existence of accidental ingestion.

Standard of proof: how convincing must the evidence be?

Closely related to the burden of proof is the standard of proof, or how convincing the evidence must be. According to Ariadna, CAS generally uses three levels:

1. Beyond a reasonable doubt – the panel must be completely convinced, leaving no room for uncertainty.
2. Comfortable satisfaction – the panel is reasonably confident, though not absolutely sure.
3. Balance of probabilities – the lowest threshold, requiring the facts to be more likely than not (i.e., >51%).

This last standard is often used in doping cases, which benefits athletes who are trying to explain positive tests due to accidental ingestion or contamination. As Ariadna notes, “It’s easier to show that something was more likely than not, rather than proving it beyond all doubt.”

Admissibility and ethical boundaries

Although CAS is generally flexible regarding admissibility, Ariadna emphasized some non-negotiable ethical limits. Illegally obtained evidence—such as private messages intercepted without consent—is not allowed. Similarly, testimonies from minors must be anonymized and handled with care.

Another key procedural rule is timeliness. Evidence must be submitted with the initial filing—whether it’s the statement of claim or the appeal brief. If new evidence arises later, the submitting party must justify why it wasn’t available earlier.

Conclusion

As Ariadna Mendoza highlights, evidence is not just a formality—it is the backbone of a winning case before the CAS. Lawyers must understand both the legal framework and the strategic considerations involved in building and presenting evidence.

“Knowing what to prove, how to prove it, and when to do so can make the difference between winning and losing,” Ariadna concluded. Her reflections offer a valuable roadmap for practitioners navigating the often-challenging terrain of international sports arbitration.