The purpose of this experiment was to investigate whether prosocial and antisocial teammate behaviors affect emotions (i.e., happiness, anxiety, anger), attention, and performance. Undergraduate sport and exercise science students (N = 102) were randomly assigned to one of three groups: prosocial behavior, antisocial behavior, and control. They performed a basketball free-throw shooting task for 2 minutes in baseline and experimental phases and completed measures of emotions and attention. Free-throw shooting performance was also recorded. A series of two group analyses of covariances controlling for baseline scores showed that the prosocial group reported more happiness than the antisocial and control groups. The antisocial group reported more anxiety than the prosocial group, and more anger and lower attention than the other two groups. The prosocial and antisocial groups performed better than the control group. These findings suggest that prosocial and antisocial teammate behaviors may influence the recipient’s emotions, attention, and performance during sport competition.