In which sport is there one poolside and two underwater referees?

Underwater hockey (UWH), also known as Octopush (mainly in the United Kingdom) is a globally played limited-contact sport in which two teams compete to manoeuvre a puck across the bottom of a swimming pool into the opposing team's goal by propelling it with a hockey stick (or pusher). A key challenge of the game is that players are not able to use breathing devices such as scuba gear whilst playing, they must hold their breath.

The game originated in England in 1954 when Alan Blake, a founder of the newly formed Southsea Sub-Aqua Club, invented the game he called Octopush as a means of keeping the club's members interested and active over the cold winter months when open-water diving lost its appeal.

Underwater hockey is now played worldwide. The first Underwater Hockey World Championship was held in Canada in 1980.

Officiating the game are two (or three) water referees (i.e. in the pool with full snorkelling gear, and wearing a distinctive red cap, orange gloves and golden yellow shirt) to observe and referee play at the pool bottom, and one or more poolside deck referees to track time (both playing times and penalty times for penalised players), maintain the score, and call fouls. The deck (chief) referee responds to hand signals given by the water referees to start and stop play, including after an interruption such as a foul or time-out, or indeed to stop play if they themself see a rule infringement.