Underwater Hockey (also known as Octopush mainly in the United Kingdom) is a globally played limited-contact sport in which two teams compete to maneuver a puck across the bottom of a swimming pool into the opposing team's goal by propelling it with a hockey stick (pusher).
The Confédération Mondiale des Activités Subaquatiques (CMAS) is the world governing body on the sport, which originated in England in 1954.
The first Underwater Hockey World Championship was held in Canada in 1980 after a false start in 1979 brought about by international politics and apartheid.
Two teams of up to ten players compete, with six players in each team in play at any one time. The remaining four players are continually substituted into play from a substitution area, which may be on deck or in the water outside the playing area, depending on tournament rules.
Before the start of play the puck is placed in the middle of the pool, and the players wait in the water whilst touching the wall above the goal they are defending. At the start-of-play signal (usually a buzzer or a gong) in-play members of both teams are free to swim anywhere in the play area and try to score by maneuvering the puck into the opponents' goal. Players hold their breath as they dive to the bottom of the pool (a form of dynamic apnoea, as in free-diving). Play continues until either a goal is scored, when players return to their wall to start a new point, or a break in play is signaled by a referee (whether due to a foul, a time-out, or the end of the period of play).
Games consist of two halves of typically ten to fifteen minutes (depending on tournament rules; 20 minutes at World Championship tournaments) and a short half-time interval of usually three minutes. At half time the two teams switch ends. A typical playing formation is 3-3 (three offensive players or forwards, and three defensive players or backs) of which 3-2-1 (three forwards, two mid-fielders and a back) is a variation. Other options include 2-3-1 (i.e., two forwards, three mid-fielders, and a back), 1-3-2, or 2-2-2. Formations are generally very fluid and are constantly evolving with different national teams being proponents of particular tweaks in formations, such as New Zealand with their 'box' (2-1-2-1) formation. As important to tournament teams' formation strategy is the substitution strategy; substitution errors might result in a foul (too many players in the play area) that can result in a player from the offending team being sent out, or maybe a tactical blunder (with too few defenders in on a play).