<p>The article examines the principle of <i>contra proferentem</i> (the interpretation of unclear provisions against their drafter) through the lens of CAS and FAT/BAT jurisprudence. It distinguishes between the interpretation of contracts and that of sports regulations. For contracts, the article argues that the contours of the principle should be defined by the applicable law, and that no automatic presumption in favour of athletes is required: a properly applied national contract law can still yield balanced outcomes, allowing ambiguity to be resolved, where justified, in favour of athletes. By contrast, in the field of sports regulation, given its complex and often unilateral nature, the article suggests that there are good reasons to recognise a distinct <i>contra proferentem sportivus</i> principle as part of transnational sports law rather than any single national regime. Where sports regulation functions as a quasi-statutory framework, combining association-law and contractual elements and sometimes taking the form of instruments detached from any one national system, it raises complex issues of characterization and applicable law. In this setting, the <i>contra proferentem</i> principle, firmly anchored in jurisprudence, can operate as a safeguard for ensuring sports justice. This transnational variant is primarily grounded in considerations of legality and proportionality. In both settings, however, the article shows that the principle is not overused in practice and suggests that its application should remain carefully conditioned and clearly justified.</p>