Football hooliganism, also known as football rioting, constitutes violence and other destructive behaviors perpetrated by spectators at association football events. Football hooliganism typically involves conflict between pseudo-tribes, formed to intimidate and attack supporters of other teams. Certain clubs have long-standing rivalries with other clubs and hooliganism associated with matches between them can be more severe. Conflict may arise at any point, before, during or after matches and occasionally outside of game situations. Participants often select locations away from stadiums to avoid arrest by the police, but conflict can also erupt spontaneously inside the stadium or in the surrounding streets. In extreme cases, hooligans, police and bystanders have been killed, and riot police have intervened. Hooligan-led violence has been called "aggro" and "bovver".