The Court of Arbitration for Sport on Friday imposed a four-year ban on American sprinter Erriyon Knighton after upholding appeals from World Athletics and the World Anti-Doping Agency against a previous decision to clear him.

The ruling from sport's highest court stems from a positive test for a banned substance that the 21-year-old sprinter argued came from contaminated meat.

Knighton's ban is effective immediately, beginning Sept. 12, 2025, but he will receive credit for a provisional suspension he served between April 12 and June 19, 2024. His competitive results from March 26, 2024, to April 12, 2024, have been disqualified.

The United States Anti-Doping Agency charged Knighton with an anti-doping rule violation on May 28, 2024, after an out-of-competition test revealed the presence of epitrenbolone, a metabolite of the banned anabolic steroid trenbolone.

An arbitration tribunal initially ruled on June 19, 2024, that Knighton should face no period of ineligibility, finding he bore "no fault or negligence" for the positive test.

World Athletics and WADA appealed that decision to CAS, arguing Knighton's evidence of a meat contamination excuse was statistically impossible and failed to prove the source of the substance.

Knighton argued during a CAS hearing in June that the positive test was caused by eating an oxtail dish contaminated with trenbolone, which is sometimes used illegally in livestock to promote growth.

The three-judge CAS panel found that his explanation was not supported by proof.

"The CAS Panel determined that there is no proof that would support the conclusion that oxtail imported into the USA would be likely to contain trenbolone residues at the level required to have caused the Athlete's Adverse Analytical Finding," the court said in a statement.

Knighton finished fourth in the men's 200-meter final at the Paris Olympics. The ban will sideline him for the 2028 Los Angeles Olympics.