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 the 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 (a Knockout , or KO) or if the opponent is deemed too injured to continue (a Technical Knockout, or TKO). 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.