This research aimed to (a) determine whether mastery and intrateam performance achievement goals predicted prosocial and antisocial teammate behavior, (b) explore whether effects of intrateam performance goals were mediated by moral disengagement, and (c) examine whether any effects (Study 2 only) were moderated by cohesion. In Study 1, team athletes (N = 282) from Australia completed questionnaires assessing the aforementioned variables. Structural equation modeling indicated that prosocial teammate behavior was positively predicted by mastery approach goals, and negatively predicted by mastery- and intrateam performance avoidance goals, whereas antisocial teammate behavior was positively predicted by intrateam performance-approach and -avoidance goals; these latter effects were mediated by moral disengagement. In Study 2, team athletes (N = 452) from the United Kingdom completed a measure of cohesion in addition to the Study 1 instruments; the analyses largely confirmed the Study 1 findings. However, the undesirable effect of mastery-avoidance goals on prosocial behavior seen in Study 1 was only apparent in Study 2 when individuals held strong perceptions of team cohesion. In sum, this investigation makes a novel contribution to the literature on team functioning in sport, being the first to explore how athletes' normative goals relative to their teammates might shape effective interaction processes.