(1) Background: The World Anti-Doping Agency (WADA) utilizes three criteria to include a technology in the List of Banned Substances and Methods—performance enhancement, health, and the spirit of sport. The latter is arguably the most fundamental one, as WADA justifies the anti-doping mission by appealing to it. (2) Method: Given the interrelationship among the notions of “human nature,” “natural talent,” and “sport,” I investigate what view of human nature underpins the “spirit of sport” criterion. To do so, I focus on (...) both WADA’s official documents and scholarly formulations of the spirit of sport (that align with that of WADA). (3) Results: I show that the value attributed to excellence and effort in WADA’s formulation of the “spirit of sport” criterion has its roots in the notion of human nature of the work ethic that resulted from the secularization of the Protestant ethic. (4) Conclusion: Drawing on my analysis of the “spirit of sport” criterion, I pose critical questions concerning the justification of WADA’s anti-doping campaign and a tentative solution to move forward in the debate. (shrink)