Answer
The Court of Arbitration for Sport overturned Chambers' lifetime Olympic ban in 2005. The ban was imposed after Chambers tested positive for the banned steroid tetrahydrogestrinone (THG) in 2003. Chambers had argued that he had taken the drug unknowingly, but the CAS ruled that he had failed to prove his innocence. The CAS's decision was controversial, and it sparked debate about the use of performance-enhancing drugs in sports.