A hooligan is a rowdy person who causes trouble for others. Hooligans are similar to bullies and thugs.
This is a slightly old-fashioned word for a troublemaker, especially a violent troublemaker. People who start a fight during a sports event are acting like hooligans. In fact, this word is used often for people who start fights at soccer matches, but anyone acting rowdy or obnoxious could be considered a hooligan. Often, hooligans are gang members or criminals. If you see a group of hooligans, it’s probably a good idea to avoid them.