Erriyon Knighton and the Contaminated-Meat Defense

Timeline

1. Mar 26, 2024An out-of-competition sample from Knighton later tests positive for epitrenbolone, a trenbolone metabolite.
2. Apr 12, 2024Knighton is provisionally suspended.
3. May 28, 2024USADA charges Knighton with an anti-doping rule violation.
4. Jun 19, 2024A US arbitrator accepts the contaminated-oxtail explanation, finds no fault and imposes no ban.
5. Jul 18, 2024The US arbitrator issues a reasoned decision relying on hair, polygraph and meat-sample evidence.
6. Aug 8, 2024World Athletics and WADA appeal to CAS; USADA does not appeal.
7. Jun 23–24, 2025CAS holds a hearing in Lausanne.
8. Sep 12, 2025CAS imposes a four-year ban.

The ethical issues

• Strict liability when banned substances may enter the food supply.
• The burden of proving the source of a substance.
• Inconsistency between national and international anti-doping bodies.
• Whether intent can be inferred when contamination is not proven.
• Fairness to clean competitors and to athletes exposed to contamination.

Stakeholders

Stakeholder	Interests & obligations
The athlete	His career, reputation and a fair hearing.
USADA	Its credibility and its handling of the first-instance case.
WADA and World Athletics' integrity unit	Consistent, credible enforcement of the rules.
Clean competitors	Fair competition and protection against implausible excuses.
Athletes generally	Protection against genuine food contamination.
Fans	Trust in results.

The case

Erriyon Knighton is an American sprinter and a world championship silver and bronze medalist.^[2] In March 2024, an out-of-competition test found epitrenbolone, a metabolite of the anabolic steroid trenbolone, in his sample.^[1][2] Trenbolone is used by athletes to build muscle mass and strength. It is also used in the US meat industry to promote muscle growth in cattle.^[2] Knighton argued that the finding came from contaminated oxtail.^[1][2]

Background

The US Anti-Doping Agency (USADA) charged Knighton on May 28, 2024. He contested the sanction before a US arbitration tribunal.^[1] In June 2024, a sole arbitrator accepted that he had eaten contaminated oxtail bought from a Florida restaurant, that it was capable of causing his positive test, and that he bore no fault or negligence. The arbitrator imposed no ban.^[1][2] His provisional suspension, served from April 12, 2024, ended on June 19.^[1]

USADA accepted the ruling and did not appeal. According to WADA, it did so “despite the evidence from its experts that this was implausible.”^[3] The ruling cleared Knighton to compete at the Paris Olympics, where he finished fourth in the 200 meters.^[5]

The rules and governance

Under the World Anti-Doping Code, an athlete is responsible for any prohibited substance in their sample. An athlete can avoid a sanction by showing no fault or negligence, which requires proving how the substance entered the body.^[1][2] For an anabolic steroid, the violation is presumed intentional, carrying four years, unless the athlete shows otherwise.^[2]

WADA reviews decisions by national agencies and can appeal to the Court of Arbitration for Sport (CAS).^[3] On August 8, 2024, World Athletics, through its Athletics Integrity Unit (AIU), and WADA appealed, seeking a four-year ban.^[1] They argued that the trenbolone concentration in meat that USADA had obtained from the same restaurant could not have caused the concentration in Knighton’s sample, that his evidence fell “short of the required proof of source on a balance of probabilities,” and that the scenario was “statistically impossible.”^[1][2] WADA called several experts, including some who had given evidence for USADA at the first hearing.^[3]

The published award shows how much turned on numbers. The laboratory reported epitrenbolone at about 1.3 ng/mL in both samples, or 1.14 ng/mL adjusted for specific gravity; with measurement uncertainty, the lowest possible value was 0.912 ng/mL.^[6] The appellants’ expert reported that a concentration of 0.1 ng/g of trenbolone in 500 grams of meat could not produce the detected level, especially in a sample collected three to four days after the meal, when most of the substance would have been excreted.^[6]

After a hearing in June 2025, the three-member CAS panel found that some assumptions made by Knighton’s experts were “highly unlikely.” The evidence did not show that imported oxtail was likely to contain trenbolone residues at the level needed to cause the finding, or that animals were treated in a way that could cause such levels.^[1][2] The scenario was not “scientifically impossible,” the panel said, but it was not “plausible” on the evidence and “certainly not more likely than not.”^[2]

The panel also found that Knighton had failed to prove a lack of intent without establishing the source. Intentional use, it held, cannot be ruled out by “a low concentration of the substance,” negative tests near the positive one, a lack of evidence of doping doses or performance effects, “a negative hair analysis or a negative polygraph test.”^[2]

On September 12, 2025, CAS imposed a four-year ban, starting that day, with credit for his earlier provisional suspension. It disqualified his results from March 26 to April 12, 2024, but rejected the request to disqualify his results through the date of the award.^[1][2]

Two tribunals, one record

The US arbitrator’s reasoned decision of July 18, 2024 shows how the same evidence could lead to opposite results.^[7] USADA had sent an investigator to the restaurant in May 2024 to buy oxtail. The receipt and packaging traced that batch to a meat-processing facility in Nicaragua, and a WADA-accredited laboratory found trenbolone in it at 0.1 ng/g.^[7] The athlete had his protein powder tested, and it was negative. Hair samples analyzed by a leading hair-testing expert were negative for trenbolone, and he passed a polygraph in which he denied ever knowingly using the drug.^[7] The arbitrator noted that he had been tested 62 times with a clean record apart from this finding, and had tested negative in the weeks before and after.^[7]

The legal dispute was over what “establish how the substance entered” requires. USADA argued, citing a line of CAS cases, that the defense fails if the concentration in the athlete’s sample does not match the claimed source. The athlete replied that such a burden “would be practically impossible to meet” in a meat case, because the meat he ate no longer exists.^[7] The arbitrator distinguished supplement cases, where the Code expressly warns athletes, noting that “No such warning exists in the Code regarding the ingestion of meat.”^[7] He relied heavily on a 2019 CAS decision that had cleared another athlete on similar evidence, and found that the athlete “did not just ‘plead and speculate’” but had set out “in a systematic way” to show he was a victim. He also said that WADA’s concern that meat contamination is “the obvious excuse” for trenbolone users “is not lost on this Arbitrator.”^[7]

The CAS panel weighed the same categories of evidence differently. For the appellants, the key fact was the arithmetic linking the oxtail’s measured concentration to the sample. The panel listed hair tests and polygraphs among factors that cannot by themselves rule out intentional use.^[2][6] USADA chose not to appeal its own loss, so the decisive challenge came from the international federation and WADA. This is the review mechanism the Code builds in to keep national outcomes consistent.^[3][4]

USADA’s response

When World Athletics and WADA appealed, USADA chief executive Travis Tygart said the agency had done “exactly what the rules demand”: it provisionally suspended Knighton, tested his B sample, charged him, and expedited the case to an independent arbitrator, with the AIU and WADA observing the hearing, and then published the full decision.^[4] He said the level in Knighton’s sample was below 1 ng/mL and that the meat came from the same supplier as restaurant meat that later tested positive for trenbolone. “The real issue in this case is WADA’s bad rule,” he said, arguing that trenbolone is “a known livestock enhancer” and that USADA had sought changes to the contamination rules for years.^[4] He contrasted the case with WADA’s handling of positive tests for trimetazidine among Chinese swimmers, which were not publicly announced (see Chinese swimmers and trimetazidine).^[4]

Aftermath

WADA said it had appealed “in the interest of fairness for athletes and clean sport,” and that it “will continue to appeal cases to CAS when it feels justice has not been served.”^[3] The decision highlighted a disagreement between USADA and WADA over how to treat the case.^[3]

The core dilemma

Meat contamination with trenbolone is possible in some food systems, and athletes cannot test every meal. But a contamination defense that is accepted too easily could become a loophole for steroid users. How should anti-doping rules handle food contamination, and how much proof should an athlete have to provide?

Competing values

• Protection of innocent athletes vs. prevention of false excuses.
• Strict liability vs. individual fairness.
• National discretion vs. international consistency.
• Scientific uncertainty vs. the need for clear decisions.

Strongest arguments

For the CAS ruling: the athlete must prove the source, and the scientific evidence showed the oxtail scenario was not plausible. Accepting weak contamination claims would undermine steroid enforcement.

Against or for reconsidering the rule: trenbolone is used legally in cattle, so contamination is real. Low concentrations and negative hair tests suggest a lack of doping intent, and presuming intent without proof of source can produce harsh outcomes.

For reform: set reporting thresholds for substances known to contaminate food, while keeping strict rules for higher concentrations.

Applying the frameworks

Justice

A justice lens asks whether it is fair to place the burden of proving the source on the athlete, and whether outcomes are consistent across national agencies and CAS.

Rights

A rights lens weighs an athlete’s right not to be punished for accidental contamination against clean competitors’ right to fair competition.

Utilitarianism

A utilitarian lens weighs the deterrent value of strict rules against the harm of wrongly banning contaminated athletes. It asks whether reporting thresholds would improve overall outcomes.

Walk it through: the Simple Decision Model

1. Spot the issue. You are WADA’s legal team deciding whether to appeal. Stakeholders include the athlete, USADA, competitors and fans. Less visible are athletes who eat meat in regions where trenbolone is used. The codes are the World Code and the international standards.
2. Gather facts. What concentrations were in the sample and in the meat? What do experts say about plausibility? Beware bias against national agencies or towards the athlete.
3. Test options. (a) Accept the first ruling. (b) Appeal to CAS. (c) Accept the ruling and propose rule changes on contamination thresholds.
4. Check codes and law. Check WADA’s appeal rights and the Code’s rules on fault and intent.
5. Decide and document. Explain the scientific and legal basis for appealing.
6. Communicate and follow up. Publish the reasons and review contamination policies.

What’s settled and what’s contested

• Settled: the positive test; the first ruling; CAS’s four-year ban.
• Contested: whether meat contamination was possible in this case; whether the burden of proving source is fair; how to handle food contamination generally.

Why this case matters

The Knighton case shows how anti-doping rules handle contamination claims and how international review can override a national decision. It is a case study in burden of proof, scientific uncertainty and consistency.

Key terms

Strict liability

The anti-doping principle that athletes are responsible for any prohibited substance in their bodies, whether or not they meant to take it.

Due process

Fair procedures before a sanction: notice, a chance to respond, an impartial decision-maker and a right of appeal.

Controls

Concrete safeguards that make ethics operational: training, disclosure forms, testing, monitoring, hotlines. Ethics needs principles, process and controls.

Trust

The public’s belief that what they are watching is real. Integrity failures are ultimately failures of trust.

Institutional accountability

Structures that make a sport organization explain its decisions and face consequences: clear authority, transparency, appeals, independent oversight and enforcement.

Definitions from the Ethics Cases glossary.

Discussion questions

1. Trenbolone is used in US cattle farming. Should athletes bear the risk of contaminated food, or should the rules set thresholds for such substances?
2. CAS said intentional use cannot be ruled out by low concentration, negative hair tests or polygraphs. Is it fair to presume intent when an athlete cannot prove the source?
3. USADA accepted the first ruling, but WADA and World Athletics appealed. What does that disagreement say about consistency in anti-doping?
4. How should the system balance protecting innocent athletes from contamination against preventing false excuses?

Sources

1. CAS upholds appeals by World Athletics and WADA to impose 4-year ban on sprinter Erriyon Knighton (media release, 12 September 2025) — Court of Arbitration for Sport
2. CAS Appeal Panel: Knighton failed to establish his ADRV was not intentional (21 October 2025) — Athletics Integrity Unit
3. WADA welcomes result of appeal in case of U.S. sprinter Erriyon Knighton — World Anti-Doping Agency
4. Statement by Travis T. Tygart in response to appeal of Erriyon Knighton case — U.S. Anti-Doping Agency
5. Erriyon Knighton ban: Sprinter handed four-year doping ban as Cas rules in favour of appeals by World Athletics and Wada (Sept. 2025) — BBC Sport
6. Arbitral award, CAS 2024/A/10800 World Athletics v. USADA & Erriyon Knighton and CAS 2024/A/10802 WADA v. USADA & Erriyon Knighton — Court of Arbitration for Sport
7. USADA v. Erriyon Knighton, New Era ADR Case No. 24052801, Reasoned Decision (July 18, 2024) — U.S. Anti-Doping Agency (published decision)