The study found that 8 percent of the variance in antisocial behavior and 7 percent of the variance in prosocial behavior could be attributed to the sporting environment, more specifically, the influence of team members and the coach. Sociomoral reasoning was significant as a contextual factor in explaining the influence of team membership on prosocial behavior; and coach-athlete relationship quality was significant as a contextual factor in explaining the influence of team membership on antisocial behavior. These findings are in accordance with research that emphasizes the important role played by the peer group, as well as studies that have shown the importance of relationship quality with parents or other important adults. Athletes who experienced a favorable sociomoral atmosphere in the sporting environment and a positive relationship with their coach reported less antisocial behavior. More prosocial behavior was predicted by positive perceptions of the sociomoral atmosphere and mature sociomoral reasoning. Results suggest that coaches who have good relationships with their athletes reduce antisocial behavior, and that exposure to relatively high levels of sociomoral reasoning within the immediate context of sporting activities promotes prosocial behavior. The participants, 153 male and 107 female athletes, were recruited from 25 teams and ranged in age from 12 to 18. Participants completed questionnaires on social desirability, antisocial and prosocial behavior, sociomoral atmosphere of the sporting environment, sociomoral reasoning about sport dilemmas, and coach-athlete relationship quality. 3 tables and 68 references