Underwater Hockey or Octopush is played on the bottom of a swimming pool using a small hand held bat - the aim is to get the lead puck into the goal with the help of your team mates.
As you can see, you need some equipment to play:
Hats Bats Glove
and obviously a swimsuit! :-)
There is no need to worry about holding your breath. You can come up for air and go back down as many times as you need to... Most people find that they are so involved in the game, that they don't think about breathing! It just happens. For more information on the game see the British Octopush Association's official site http://www.gbuwh.co.uk