This document summarizes a study on how social identity influences behavior. In the first part, Manchester United supporters were more likely to help a runner who had tripped if they were wearing a Manchester United shirt, compared to a Liverpool shirt or plain shirt. In the second part, when primed to think of their identity as football fans rather than a specific team, participants were equally likely to help a runner wearing any football shirt. The study shows that social identity can be situationally primed and affects how helpful people are toward in-group or out-group members.