The case involves Heiki Nabi, an Estonian wrestler, who appealed a decision by the Estonian Center for Integrity in Sports (ESTCIS) after testing positive for Letrozole, a prohibited substance. The Court of Arbitration for Sport (CAS) reviewed the case, focusing on whether Nabi could prove the substance entered his system unintentionally. Nabi proposed several contamination scenarios, including contaminated meat, exposure through sweat or saliva, and tainted gym equipment. However, the panel found these explanations lacked sufficient scientific evidence or documented cases to support them. The panel emphasized the strict liability principle in anti-doping regulations, which holds athletes responsible for any prohibited substance in their system, regardless of intent. Nabi argued that identifying the exact source of contamination was impossible, invoking the legal principle "Ultra posse nemo obligatur" (no one is obliged beyond what they are able to do). He also cited expert testimonies, hair analysis, and polygraph results to demonstrate his lack of intent. While the panel acknowledged the low concentration of Letrozole suggested incidental exposure, it ruled that Nabi failed to meet the burden of proof required to reduce or eliminate his two-year ineligibility period under Articles 10.5 or 10.6 of the Estonian Anti-Doping Rules (EADR). These articles allow for sanction reductions if the athlete can prove no fault or negligence or no significant fault or negligence, but they require the athlete to establish how the substance entered their system. The panel rejected Nabi's proportionality argument, stating the rules already account for fairness through these provisions. Despite expressing discomfort with the outcome, the panel upheld the original decision, underscoring the stringent application of anti-doping regulations. The case highlights the challenges athletes face in proving unintentional violations and the high evidentiary standards required to contest doping sanctions. The CAS dismissed Nabi's appeal, confirming the two-year suspension and maintaining the integrity of anti-doping enforcement.