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. Water polo is a very violent and aggressive sport. Minor fouls occur frequently and exclusion fouls (in which a player is suspended from the game for 20 seconds) are common. 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), using a special form of treading water known as the eggbeater kick (to position a player upright in the water), throwing, catching, and shooting the ball using a single hand. Each team consists of 6 field players and a goalkeeper. Except for the goalkeeper, players participate in both offensive and defensive roles. The players are also required to have some ability to play in all offensive and defensive roles. 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.