Boxing is a combat sport in which two participants of similar weight fight each other with their fists. Boxing today is conducted in a regulated way, typically in a series of one to three-minute intervals called rounds. Victory is achieved if the opponent is knocked down 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.