Two teams of up to ten players compete, with six players in each team in play at any one time.[3] The remaining four players are continually substituted into play from a substitution area, which may be on deck or in the water outside the playing area, depending on tournament rules.
Before the start of play the puck is placed in the middle of the pool, and the players wait in the water whilst touching the wall above the goal they are defending. At the start-of-play signal (usually a buzzer or a gong) in-play members of both teams are free to swim anywhere in the play area and try to score by manoeuvring the puck into the opponents' goal. Players hold their breath[4][5] as they dive to the bottom of the pool (a form of dynamic apnoea, as in free-diving). Play continues until either a goal is scored, when players return to their wall to start a new point, or a break in play is signalled by a referee (whether due to a foul, a time-out, or the end of the period of play).