According to self-categorization theory , incidents of crowd violence can be understood as discrete forms of social action, limited by the crowd's social identity. Through an analysis of the riot at Woodstock 1999, this paper explores the uses and limitations of SCT in order to reach a more complex psychology of crowd behavior, particularly those instances that appear unmotivated, irrational, and destructive. Psychological and sociological literature are synthesized to explore the role of communication in establishing social norms within the crowd. Several modifications to current crowd psychology are proposed, including a false consensus effect of motivation and the mediation of personal and social identities.