Players tread water the entire game and cannot touch the bottom or sides of the pool. Except for the goalkeeper, players may handle the ball with only one hand. In the case of a tie, two three-minute periods of overtime are played. If the score is tied after overtime, sudden-death overtime is played.
Substitutions are most common after a goal is scored, between periods, or for an ejected player.
Players can also substitute by swimming to their bench corner and tagging an entering player. Each team is allowed three time-outs during regulation. Physical contact is the rule rather than the exception, as the players maneuver for position in front of the goal. The referee indicates fouls by blowing a whistle and using hand signals to point out the location of the foul and the attacking direction of the fouled player. Unlike most sports that stop on a whistle, action in water polo is initiated by the whistle.