Read the passage carefully, then choose the correct answer: 
Underwater hockey is a non-contact sport in which two teams compete to maneuver a puck across the bottom of a swimming pool into goals. 
Players wear a diving mask, fins, speedos and a snorkel for play_ Safety gear includes a water polo style cap, a mouthguard, and a glove for the playing hand (to protect against pool-bottom abrasion and, in some designs, knuckle protection against puck impact). Because current rules permit a player to switch the stick between hands mid-play, players may choose to wear a protective glove on both hands. The stick is quite short (not more than 350 mm in length, including the handle) and is colored white or black to indicate the player's team.
Two teams of up to ten players compete, with six players on each team in play at once. Substitution happens continually from a substitution area, which may be on deck or in the water outside the playing area, depending on tourna went rules. Before the start of play the puck is placed in the middle of the pool, and the players wait in the water, touching the wall above the goals they are defending. At the start-of-play signal, in- play members of both teams are free to swim anywhere in the play area and try to score by sending the puck into the opponents' goal. Play continues until either a goal is scored, and players return to their wall to start a new point, or a break in play is signaled by a referee. 
There are a number of penalties described in the official underwater hockey rules, ranging from use of the stick against something (or someone) other than the puck or the playing surface, playing or stopping the puck with something other than the stick, and "screening". If the penalty is minor, referees award an advantage puck - the team that committed the foul is pushed back 3 meters from the puck, while the other team gets a free possession. For major penalties, such as a dangerous pass or intentional or repeated fouls, the referees may eject. players for a specified period of time or the remainder of the game. A defender committing a serious foul sufficiently close to his own goal may be penalized by the award of a point to the fouled player's team.
Games consist of two halves, typically ten to fifteen minutes in length (depending on tournament rules; 15 minutes at world championship tournaments) and a short half time interval. At half time the two teams switch ends.

How many people compete in, the game?

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