Boxing is a combat sport and martial art in which two people fight using their fists. Boxing is typically supervised by a referee engaged in during a series of one- to three-minute intervals called rounds, and boxers generally of similar weight. There are three ways to win; if the opponent is knocked out and unable to get up before the referee counts to ten seconds or if the opponent is deemed too injured to continue. If there is no stoppage of the fight before an agreed number of rounds, a winner is determined either by the referee's decision or by judges' scorecards.