Abstract: Coaches of professional sports teams are often credited or blamed for the success or failure of their teams, and they are compensated as if they are one of the most important features of a franchise. Although we have anecdotal evidence that coaches matter, the sports analytics literature has generally concluded that they do not. We present a new method for estimating coach effects, which we call Randomization Inference for Leader Effects, or RIFLE. We apply RIFLE to the MLB, NBA, NHL, NFL, college football, and college basketball. We detect coaching effects in all sports. Our estimates generally imply that coaches explain about 20-30 percent of the variation in a team’s success, although coaching effects vary notably across settings and across various outcomes. For example, baseball managers affect runs allowed more than runs scored. Coaches matters more in college football than in the NFL, but do not meaningfully differ in their use of rushing vs. passing. In addition to estimating average coaching effects, we also discuss the difficult task of assessing the quality of an individual coach.