Water polo, or Water ball, is a team water sport. The playing team consists of six field players and one goalkeeper. The winner of the game is the team that scores the most goals. Game play involves swimming, treading water (using a sort of kicking motion known as "eggbeater kick"), players passing the ball while being defended by opponents, and scoring by throwing the ball into a net defended by a goalie. 'Man-up' (or 'power play') situations occur frequently. Water polo, therefore, has strong similarities to the land-based game of team handball.
Seven players from each team (six field players and a goalkeeper) are allowed in the playing area of the pool during game play with up to four substitutes. Visiting team field players wear numbered and usually White caps, and home team field players wear usually Blue caps (though any other contrasting colors are now allowed); both goalies wear red caps, numbered "1". Players may be substituted in and out after goals, during timeouts, at the beginning of each quarter, after ordinary fouls and after injuries. During game play, players enter and exit in the corner of the pool, or in front of their goal; when play is stopped, they may enter or exit anywhere.
If an offensive player, such as the hole set (center forward), has possession of the ball in front of the goal, the defensive player tries to steal the ball or to keep the center from shooting or passing. If the defender cannot achieve these aims, he may commit a foul intentionally. The hole set then is given a free throw but must pass off the ball to another offensive player, rather than making a direct shot at the goal. Defensive perimeter players may also intentionally cause a minor foul and then move toward the goal, away from their attacker, who must take a free throw. This technique, called sloughing, allows the defense an opportunity to double-team the hole set and possibly steal the inbound pass. The referee may refrain from declaring a foul, if in his judgment this would give the advantage to the offender's team. This is known as the Advantage Rule