Number of Players
Seven players from each team (six field players and a goalkeeper) are allowed in the playing area of the pool during game play. Each team may also have six additional substitute players, and up to one of these players may take the position of the reserve goalkeeper. If a player commits a major foul, then that team will only have 6 players until the player is allowed to re-enter. If a player commits a brutality foul, then that team must play without that player, or any player taking his or her place, for 4 minutes.
If at any time during play a team has more players in the pool than they are allowed, a penalty is given to the opposing team.
The two opposing teams must wear caps which contrast:
- with both (or either) goalkeeper cap color
- with the other team's cap color and with the ball color
In practice, one team usually wears blue caps and the other white, but some teams do choose to wear different cap colors. For instance, Australia's women's water polo team wears green caps.
Both goalies wear red caps. The first choice goalkeeper is usually marked "1" with the reserve being marked "13" (under FINA rules) or "1A" (under NCAA and NFHS rules). 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.
Duration of Game
The game is divided into four periods; the length depends on the level of play.
Game and Shot Clock
The game clock is stopped when the ball is not 'in play' (between a foul being committed and the free throw being taken, and between a goal being scored and the restart). As a result, the average quarter lasts around 12 minutes 'real time'. A team may not have possession of the ball for longer than 30 seconds without shooting for the goal unless an opponent commits an ejection foul. After 30 seconds, possession passes to the other team. However, if a team shoots the ball within the allotted time, and regains control of the ball, the shot clock is reset to 30 seconds. Each team may call 1 one-minute timeout in each period of regulation play, and one timeout if the game goes into overtime. During game play, only the team in possession of the ball may call a timeout.
Dimensions of the water polo pool are not fixed and can vary between 20×10 and 30×20 meters. Minimum water depth must be least 1.8 meters (6 feet), but this in reality is sometimes not the case due to practicalities. The goals are 3 meters wide and 90 centimeters high. Water polo balls are generally yellow and of varying size and weight for juniors, women and men. The middle of the pool is designated by a white line. Before 2005, the pool was divided by 7 and 4 meter lines (distance out from the goal line). This has been merged into one 5 meter line since the 2005–2006 season. Along the side of the pool, the center area between the 5 meter lines is marked by a green line (if marked at all). The "five meters" line is where penalties are shot and it is designated by a yellow line. The "two meter" line is designated with a red line and no player of the attacking team can receive a ball inside this zone.