Abstract: Contaminant ingestion of anti-doping rule violations occurs when athletes passively consume prohibited substances through certain contaminated sources or intermediaries, resulting in positive test results. It can be classified into five types: contaminated product, contaminated meat, close contact, other contamination, and unknown sources. Through an empirical analysis of the relevant arbitral awards of the Court of Arbitration for Sport in the past decade, this study summarizes the actual factors that determine the reduction or elimination of the period of ineligibility and their logical connections at the de facto level, and contrasts them with the de jure requirements in the World Anti-Doping Code, forming an ineligibility period reduction or elimination model that includes “the logic flowchart for ineligibility period determination,” “checklist of factors of unintentional doping,” and “checklist for degree of fault assessment.” This model not only benefits the Court of Arbitration for Sport and the World Anti-Doping Agency in elevating work efficiency and quality but also enables athletes to enhance their awareness of preventing contaminant ingestion in advance and actively strive for the reduction or elimination of the period of ineligibility to safeguard their legitimate rights and interests afterwards.