The Earth team sport followed devotedly by Captain Jonathan Archer, who keeps a water polo ball in his quarters and watches recordings of matches sent from home.
Water polo, played by two teams in a swimming pool, is Archer's great sporting passion in Star Trek: Enterprise. He is often seen in his quarters bouncing a ball off the wall while thinking, with his dog Porthos looking on.
Matches from Earth reach the ship as recordings. In Vox Sola, Trip Tucker obtains footage of a championship game for the captain, and the two sit down to watch it together before an alien organism in the cargo bay interrupts.
The sport remains a quiet character note for Archer throughout the series, a link to an ordinary life on Earth during a mission that takes him ever further from it.