1. Three Degrees of Fouls: Ordinary, Exclusion and Penalty.
An ordinary foul usually just means pushing off another player, or throwing or shooting the ball out of bounds. A player can pretty much commit unlimited ordinary fouls in a game.
An exclusion foul is more serious. It commonly gets called when a defender dunks or pulls on an offensive player from behind. It can also be called when an offensive player drives (swims fast) through the middle and a defender grabs him and tries to stop or slow him down.
When a referee whistles and calls an exclusion foul, the excluded player has to swim over to the side of pool and wait there for 20 seconds while the other defenders try to keep the offense from scoring—now with one missing player. This is called a "6 on 5" situation.
A penalty foul is even more serious. Referees usually make this call when a defender commits a foul on an offensive player who is about to score a "probable goal." After a penalty foul is called, everyone has to clear out except for the defending goalie and one offensive player. The offensive player then shoots at the goal from 5 meters out while the goalie tries to block the shot.
2. Personal Fouls.
Exclusion Fouls + Penalty Fouls = Personal Fouls.
Each player is allowed 2 personal fouls. If a player commits a third personal foul, he or she has to sit out for the rest of the game. The people at the score table keep track of everyone's personal fouls in a book.
3. Whistle and Point.
Every time a referee blows the whistle, he or she will point in one direction or the other to show who gets the ball.
4. All Those Whistles!
There are some exceptions, but generally this is how whistles work:
One whistle = defensive foul or someone threw the ball out of bounds. Everyone has to back off and an offensive player gets a "free throw (or pass)" to another offensive player.
Two whistles = offensive foul. The offensive players have to drop the ball immediately and swim back the other way while the defense now becomes the offense and gets a free throw.
More than two whistles = exclusion foul. Some refs get very fancy with these exclusion whistles. Just understand that if you hear a bunch of whistles, it means someone has just been excluded for 20 seconds.
Big, long whistle = penalty foul or goal scored.
5. Two-meter (aka Goal Box) and Six-meter Lines
There are two imaginary lines crossing the pool usually marked on each side of the pool by traffic cones. One line is 2 meters out from the goal line and the other is 6 meters out.
The 2 meter area is shaped similar to a penalty box in soccer.
No offensive player can go into the defenders' 2-meter area unless the ball is already there. If that happens, it's a turnover. This explains why the offensive players can't just all swim in and crowd the goalie.
The 6-meter line has a different purpose. If the referee calls a foul when the player with the ball is outside the 6-meter line, the defender has to back off and the offensive player can shoot at the goal instead of passing to another player. The shot has to be immediate. If the player hesitates or double pumps before shooting, the referee will call a turnover.
6. The Advantage Rule: Super Important!
This rule requires referees to call or refrain from calling a foul in order to help the offense control the game flow. Sometimes, you'll see a foul happen but the referee doesn't blow the whistle because making the call would create a disadvantage for the offense.
7. Hand Signals.
After a goal is scored or an exclusion foul is called, the referees will use quick hand signals to tell the score table the cap number of the player who scored or got kicked out.
8. Goal!
The entire ball has to go across the goal line completely for a goal to count.
9. Getting the Boot aka Getting a Red Card
If a player is too aggressive or a coach behaves badly, the referee can kick that person out for the rest of the game. If this happens, that player or coach has to sit out the next game as well. Bad, bad!
10. Ball Under.
If an offensive player is holding the ball and a defender forces the ball completely under water, the referee will whistle twice (offensive foul) and award possession of the ball to the defense. This rule forces the offense to protect the ball and keep it moving.
11. The 30-Second Shot Clock.
When the offense takes control of the ball, they get 30 seconds to shoot at the goal. If they don't shoot within that time, they lose the ball (offensive foul, two whistles). The score table will reset the shot clock after a goal, a missed shot, a change of possession, an exclusion foul or at the end of a quarter.
12. Blocked Shots.
If a goalie blocks a shot and the ball goes out of the bounds, the offense gets the ball back with a new 30-second shot clock. If, however, any other defender blocks the ball out of bounds on a shot, possession of the ball goes to the defense. This is called a field block. Weird, huh?
And that's everything you need to know to enjoy a water polo game from the stands!