Water polo is a team water sport. It is the oldest continuous Olympic team sport. The playing team consists of six field players and one goalkeeper with a maximum of six substitutes. The winner of the game is the team that scores more goals. Gameplay involves swimming, players passing the ball while being defended by opponents, and scoring by throwing into a net defended by a goalie. Water polo, therefore, has strong similarities to the land-based game of team handball. The frequency of 'man-up' (or 'power play') situations also draws comparisons with ice hockey.
Seven players from each team (six field players and a goalkeeper) are allowed in the playing area of the pool during game play. Visiting team field players wear numbered and usually white caps, and home team field players wear usually dark blue caps (though any other contrasting colors are now allowed); both goalies wear quartered red caps, numbered "1". Both teams may substitute players. During game play, players enter and exit in the corner of the pool, or in front of their bench; when play is stopped, they may enter or exit anywhere.
The game is divided into four periods; the length depends on the level of play:
Level of play
Time each period
US High School
US High School
US High School
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 2 one-minute timeouts in the four periods 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 x 10 and 30 x 20 meters. Minimum water depth must be least 1.8 meters (6 feet), but this is often waived for age group or high school games if such a facility is unavailable. The goals are 3 meters wide and 90 centimetres 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. In the past, 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. The "five meters" line is where penalties are shot and it is designated by a yellow line. The "two meters" line is designated with a red line and no player of the attacking team can be inside this line without the ball.
One player on each team is designated the goalkeeper, assigned to deflect or catch any shots at goal. The goalkeeper is the only player who can touch the ball with both hands at any time, and, in a shallow pool, the only player allowed to stand on the bottom. Players can move the ball by throwing it to a teammate or swimming while pushing the ball in front of them. Players are not permitted to push the ball underwater when being tackled, or push or hold an opposing player unless that player is holding the ball. Fouls are very common, and result in a free throw during which the player cannot shoot at the goal unless beyond the "5 meter" line. If a foul is called outside the 5 meter line, the player is either able to shoot or pass the ball. Water polo players need remarkable stamina due to the considerable amount of holding and pushing that occurs during the game, some allowed, some unseen or ignored by the referees (usually underwater). Water polo is a physically demanding sport; action is continuous, and players commonly swim 3 kilometers or more during four periods of play.
Water polo is a game requiring excellent eye-hand coordination. The ability to handle and pass the ball flawlessly separates the good teams from the great teams. A pass thrown to a field position player is preferably a "dry pass" (meaning the ball does not touch the water) and allows for optimal speed when passing from player to player with fluid motion between catching and throwing. A "wet pass" is a deliberate pass into the water, just out of reach of the offensive player nearest the goal (the "hole set") and his defender. The hole-set can then lunge towards the ball and out of the water to make a shot or pass. A goal may be scored by any part of the body except a clenched fist, or a foot.
Scoring in water polo can be quite different than in other sports. For example, a "skip" or "bounce shot is fired intentionally at the water with considerable force so it will bounce back up. The ball usually hits the water within a metre of the net, where the goalie cannot anticipate and block the shot. Another shot, called a "lob" is thrown with a large vertical arc. Often these shots are more difficult to stop than a faster shot, as they are usually thrown across a net at such an angle the goalie must not only shift position from one side of the net to the other quickly, but also at the same time propel out of the water more than for other shots. Pump faking is effective when using any kind of shot. The player gets in the position to shoot but stops halfway through his motion, causing the defending goalkeeper to commit too early to block the subsequent shot.
The referee's whistle for a foul is heard much more in water polo than in other sports. A defender will often foul the player with the ball as a tactic to disrupt the opponent's ball movement. Play continues uninterrupted in most cases, but the attacker must now pass the ball instead of advancing or taking a shot. (An exception allows players to quickly pick up the ball and shoot if fouled outside of the five meter mark.) However, as in ice hockey, a player caught committing a major foul, is sent out of the playing area with his team a man-down for 20 seconds, but may return sooner if a goal is scored or his team regains possession. If the foul is judged to be brutal, the player is ejected for the remainder of the game, with substitution by another teammate after four minutes have elapsed. A player, coach or spectator can also be ejected for arguing with the referees. During a man up situation resulting from an ejection foul, the attacking team can expect to score by passing around to move the goalkeeper out of position. A player that has been ejected three times must sit out the whole match with substitution.
Swimming: Water polo is a team water sport requiring an ability to swim. Field players must swim end to end of a 30-meter pool non-stop many times during a game without touching the sides or bottom of the pool. The front crawl stroke used in water polo differs from the usual swimming style in that water polo players swim with the head out of water at all times to observe the field. The arm stroke used is also a lot shorter and quicker and is used to protect the ball at all times. Backstroke is used by defending field players to track advancing attackers and by the goalie to track the ball after passing. Water polo backstroke differs from swimming backstroke; the player sits almost upright in the water, using eggbeater leg motions with short arm strokes to the side instead of long straight arm strokes. This allows the player to see the play and quickly switch positions. It also allows the player to quickly catch an oncoming pass with a free hand.
Ball handling skills: As all field players are only allowed to touch the ball with one hand at a time, they must develop the ability to catch and throw the ball with either hand and also the ability to catch a ball from any direction, including across the body using the momentum of the incoming ball. Experienced water polo players can catch and release a pass or shoot with a single motion. The size of the ball can overwhelm a small child's hand making the sport more suitable for older children. There are also smaller balls that can be used by younger children when playing.
Treading water: The most common form of water treading is generally referred to as "egg-beater", named because the circular movement of the legs resembles the motion of an egg-beater. Egg beater is used for most of the match as the players cannot touch the bottom of the pool. The advantage of egg-beater is that it allows the player to maintain a constant position to the water level, and uses less energy than other forms of treading water such as the scissor kick, which result in the player bobbing up and down. It can be used vertically or horizontally. Horizontal egg-beater is used to resist forward motion of an attacking player. Vertical eggbeater is used to maintain a position higher than the opponent. By kicking faster for a brief period the player can get high out of the water (as high as their suit—below their waistline) for a block, pass, or shot.
Reflexes and Awareness: At higher levels of the sport the pace of play rapidly increases, so that anticipation and mental preparation is important. "Field sense" (i.e. staying aware of the surroundings) is a major advantage in scoring, even if a player lacks the speed of an opponent. 
There are seven players in the water from each team at one time. There are six fielders and one goalkeeper. Unlike most common team sports, there is little positional play; field players will often fill several positions throughout the game as situations demand. These positions consist of the center or set position, the flat, the wing and the point positions. Players who are skilled in all of these positions on offensive or defensive are called utility players. Utility players tend to come off of the bench, though this isn't absolute. Certain body types are more suited for particular positions, and left-handed players are especially coveted on the right-hand side of the field, allowing teams to launch 2-sided attacks.
The offensive positions include: one center (a.k.a. two-meter offense, hole set, hole man, bucket, pit player or pit-man), two wings, two drivers (also called "flats"), and one "point" man, positioned furthest from the goal. The center directs the attack, and the wings, drivers and point are often called the perimeter players.
The most basic positional set up is known as a 3-3, due to the fact that there are two lines in front of the opponent's goal, both containing three players. Another set up, used more by professional teams, is known as an "arc," umbrella, or mushroom; perimeter players form the shape of an arc around the goal, with the center forward as the handle or stalk. Yet another option for offensive set is called a 4-2 or double hole; there are two center forward offensive players in front of the goal. Double hole is most often used in "man up" situations, or when the defense has only one skilled hole D, or to draw in a defender and then pass out to a perimeter player for a shot ("kick out").
The center forward sets up in front of the opposing team's goalie and usually scores the most individually (especially during lower level play where perimeter players do not have the required strength to effectively penetrate and then pass to teammates like the point guard in basketball). The center's position nearest to the goal allows explosive shots from close-range ("step-out" or "roll-out", "sweep," or backhand shots).
Defensive positions are often the same positionally, but just switched from offense to defense. For example, the center forward or hole set, who directs the attack on offense, on defense is known as "hole D" ( a.k.a. hole check, pit defense or two-meter defense), and guards the opposing team's center forward (also called the hole). Defense can be played man-to-man or in zones, such as a 2-4 (four defenders along the goal line). It can also be played as a combination of the two in what is known as an "M drop" defense, in which the point defender moves away ("sloughs off") his man into a zone in order to better defend the center position. In this defense, the two wing defenders split the area furthest from the goal, allowing them a clearer lane for the counter-attack if their team recovers the ball.
The goalkeeper is generally one of the more challenging positions. A goalie has to be able to jump out of the water, using little more than one's core and legs, and hold the vertical position without sinking into the water, all while tracking and anticipating a shot. The goal is 30 square feet (2.8 m2) in face area; the goalie should also be a master of fast, effective lateral movement in the water as well as lightning fast lunges out of the water to deflect a shot. Another key job that the goalkeeper is responsible for is guiding and informing his or her defense of imposing threats and gaps in the defense, and making helpful observations to identify a gap in the defense that the defenders may or can not see.
The goalkeeper is given several privileges above those of the other players, but only if he or she is within the five meter area in front of his goal:
The ability to touch the ball with two hands.
The ability to strike the ball with a clenched fist.
The ability to touch the bottom of the pool. (Pool depth permitting)
The goalkeeper also has one limitation that other players do not have: he or she cannot cross the half-distance line. Also, if a goalie pushes the ball under water, it is not a turnover like with field players. It is a penalty shot, also called a 5-meter shot, or simply, a "5-meter".