Previous research suggests that the relation between sport participation and alcohol use is positive, but small in size. Few explanations for this positive relation have been empirically tested. Theories denote that the relation between sport participation and alcohol use is explained by peers and that the relation varies based on the models adolescents are exposed to. This study tested mediators (popularity and friends' alcohol use) and moderators (sport-focus, teammates' alcohol use, gender, popularity, and friends' alcohol use) for the relation between sport participation and alcohol use. Analyses were conducted through path models in Mplus v5.1. The sample included 48,390 adolescents (mean age=15.8 years; 51% female) from the National Longitudinal Study of Adolescent Health. In the self-administered in-school questionnaire, adolescents reported on their activity participation, alcohol use, friendship nominations, and demographic characteristics. Friend indicators were based on friends' self-reported alcohol use. Results suggested that popularity mediated, but did not moderate the relation between sport participation and alcohol use. In contrast, friends' alcohol use moderated, but did not mediate this relation. The relation was positive and strongest for sport-focused adolescents, and for adolescents whose teammates and sport friends used high levels of alcohol. The findings of this study suggest athletes are at an elevated risk for alcohol use, but not all athletes drink. Peers are important predictors, such that, sport participation may be related to alcohol use, partially, because it promotes adolescents' social status. The sport context is also important, such that, athletes are more likely to use alcohol if they are highly involved in sports, and they have sport friends and teammates who drink. Specific types of athletes, such as popular athletes, should be targeted for alcohol use interventions. Intervention programs should also be designed to capture specific aspects of the sport context, such as teams without no tolerance substance use policies, and highly competitive or stressful sports.