This paper explores a question of superficial triviality: when sports use instant replay technology to review on-field calls, what standard of review should they employ? The conventional view is that on-field calls should be entrenched against reversal such that, if the reviewing official has any doubt about the correctness of the initial call, he must let it stand even if he thinks it very probably wrong. Indeed, in the wake of officiating debacles at last summer‟s FIFA World Cup, commentators proposed not only that soccer employ instant replay, but also that it follow the NFL in directing officials to overturn on-field calls only when “indisputable visual evidence†(IVE) reveals that call to be mistaken. This essay argues that common wisdom in favor of IVE overlooks important considerations against entrenchment and likely rests upon mistaken premises, and it offers several concrete proposals for reform. A lengthy investigation into the optimal standard of review for instant replay in sports might seem frivolous. But it serves a deeper ambition. We are in the early years of sports‟ colonization by econometricians, as legal theorists remain watching from the sidelines. That is unfortunate. Formal organized sports are, in effect, legal systems, and legal theorists might find much both to teach and to learn by paying closer attention to competitive athletics. In short, legal theorists would benefit from a sustained engagement with what I have termed, in previous work, “the jurisprudence of sport.†As a case study in this nascent field, this essay reveals that the problem of appellate review in sports is surprisingly rich and complex—implicating profound questions concerning the relationships among desert, entitlement and justice; the difference between mistake and error; and the contours of loss aversion and omission bias, among other things. But it shows even more than that. The jurisprudence of sport maintains that sporting practices and norms can teach lessons for ordinary legal systems as surely as ...