An awesome sport where the objective is to drown. No one knows where the ball comes in. It's unknown as to why anybody would participate in it. Fighter McWarrior competed in the competition, and although he was a favorite to drown first because of his heavy armor, he survived because his brain uses less oxygen. Although the rules stated the player had to drown to win, the fact that Fighter was the only survivor made him the winner by default.
The game is a parody of Blitzball from Final Fantasy X. The minigame is Spira's most popular sport, and is essentially underwater rugby. The playing field is a giant, transparent sphere filled entirely with water, forcing the players to hold their breath the entire playtime. (There is another stadium shown in-game which only fills halfway, but it is destroyed minutes into plot of the game. At any rate, players are not shown surfacing to breathe in that stadium either.) The parallels are enforced by the screenshot of the Luca dome (the stadium the mini-game takes place in) during Drownball's introduction. The fact that the sport is also incredibly stupid and holds all the people's captivation may be a reference to the difficulty of the Blitzball side-quest and how much the characters of Final Fantasy X love the sport.