In the current study we aimed to examine the antecedents and outcomes associated with the variability in competitive volleyball players' (N = 67; M-age = 19.45; SD = 5.13) situational achievement goal pursuit and its underlying autonomous and controlling reasons. Players were followed during six consecutive games and data were analyzed through multilevel modeling. Players' dominant contextual goal pursuit reported at the onset Of the study related to their situational (i.e., game-specific) goal pursuit. Further, variation in game-to-game mastery-approach goal pursuit, as compared with the pursuit of other achievement goals, related to variation in prosocial behavior. Finally, autonomous reasons underlying situational mastery-approach goal pursuit related positively to games-specific prosocial behavior, enjoyment, and performance satisfaction. The discussion emphasizes the necessity to study players' game-to-game motivational dynamics and the reasons underlying players' achievement goal pursuit.