Football hooliganism is unruly, violent, and destructive behaviour by overzealous supporters of association football clubs, including brawling, vandalism and intimidation. Football hooliganism normally involves conflict between gangs, often known as football firms (the term derives from the British slang for a criminal gang), formed for the specific purpose of intimidating and physically attacking supporters of other teams. Other terms commonly used in connection with hooligan firms include "army", "boys", "casuals", and "crew". Certain clubs have long-standing rivalries with other clubs (usually, but not always, geographically close) and hooliganism associated with matches between them (sometimes called local derbies), is likely to be more severe.