AbstractThis study addresses violence of fans during football matches. It focuses on group dynamics and sociodemographic variables as determinants of serious disturbances. Overall, 505 male and female football fans, who were either ‘fanatic’ or ‘moderate’ fans from Naples and Bologna, Italy, completed a questionnaire on attitudes towards football and violence in stadiums, and related matters, and gave self‐descriptions and descriptions of their own and other football clubs. It was hypothesized that, if ‘fanatic’ fans identify more strongly with their club than ‘moderate’ fans do, they should discriminate more sharply between the fan clubs and more likely participate in disturbances. Violent behaviour was also assumed to depend on the norms associated with different fan clubs. Moreover, participation in disturbances was hypothesized to depend on sociodemographic variables. The results suggest that individuals become more aggressive in groups, that the behaviour is controlled by group norms and, hence, that aggression depends on the group's acceptance of violence. The study also supports a rather traditional picture of ‘hooligans’: the football fans who participate in disturbances are, in general, young, unemployed, poorly educated fanatics who attributed their violenc