The aim of the present study is to explore the relationships between cognitive–behavioral patterns of perfectionism in the context of competitive sport and both prosociality and aggressiveness in a sample of adolescents competing in federated sports. A cross-sectional and non-randomized study was designed using a selective methodology on a sample of adolescents (N = 234) competing in federated sports. Scales to assess aggressiveness, perfectionism, prosocial behavior, and competitiveness were administrated. The results show that as age increases, prosocial behaviors increase and aggressive behaviors and competitiveness decrease, while there was no one significant perfectionist tendency. Competitiveness showed a direct relationship with aggressive (positive) and prosocial behaviors (negative). Self-oriented perfectionistic behavior showed a direct and significant relationship with prosocial behaviors, but no significant relationship with aggressive responses. As P-SP and P-OD tendencies increased, significantly smaller links were shown with prosocial behaviors, but greater links were shown with aggressive behaviors. A path (mediation) model showed a positive and predictive relationship with aggressive behaviors and a negative relationship with prosocial altruistic behaviors. The negative influence of criticism from significant figures in their environment and unrealistic expectations about their performance are relevant to difficulties in self-regulating social relationships in adolescents. Hence, it is a challenge to promote prosocial resources (as a protective value for aggressive behaviors) in the face of the early angst of young athletes, who put their maturity to the test under conditions of high pressure and demands. The present study continues to reinforce the line drawn on perfectionism and prosocial development in young people in sports contexts where young people, measured early on according to their performance, can accentuate and deepen competitive tendencies that alter their adaptive and self-regulatory capacities, as well as their psychosocial projection.