Physical and psychological harm as a result of unsanctioned aggression and violence in sport continues to be a cause for concern. This article critically reviews and synthesizes contemporary scientific research on unsanctioned aggression and violence in amateur sport. The authors identify the need to understand violence in amateur sport within its social ecology. The proposed framework sensitizes researchers, policymakers, and practitioners to the multi-level web of interacting influences on unsanctioned aggression and violence in amateur sport, as well as to factors and issues to be considered in relation to the prevention and mitigation of violent behavior in amateur sport. The findings indicate that there is a dearth of studies that analyze the meanings and narratives of aggression and violence created by amateur sports participants themselves. The article proposes that situational approaches and, in particular, the role of bystanders offer promising directions for future research, policy, and practice concerning unsanctioned aggression and violence in amateur sport.