Water polo is a team water sport. The game consists of 4 quarters (or periods) in which the two teams attempt to score goals by throwing the ball into their opposition's goal, with the team that scores the most goals winning the game. A team consists of 6 field players and one goalkeeper in the water at any one time. In addition to this, teams may have substitute players (up to six under most governing bodies), including up to one substitute goalkeeper. Water polo is typically played in an all-deep pool (usually at least 1.8m deep), and players need considerable stamina and endurance to play the game.
Special equipment for water polo includes a water polo ball, which floats on the water; numbered and colored caps; and goals resembling a hockey goal in appearance, which either floats in the water or is attached to the side of the pool.
The game consists of swimming (with and without the ball), treading water, and throwing, catching, and shooting the ball using a single hand. Except for the goalkeeper, players do not tend to be assigned to either an attacking or defensive role. However, it is commonplace that players will play in either of these positions when required throughout the match.
The game is thought to have originated in Scotland in the late 19th century as a sort of "water rugby". William Wilson is thought to have developed the game during a similar period. The game thus developed with the formation of the London Water Polo League and has since expanded, becoming widely popular in various places around the world, notably mainland Europe, the United States of America, China, Canada and Australia.