This game is most fun in the water, but can be played on the ground too, where its not that physical hard, but still rather violent.
Make two teams. Each participant gets a balloon.
The game is about smashing the balloons of the other team, while protecting your own. The losing team is the one first without balloons.
The teams can create a group of defenders, that could surround all the team balloons, while a smaller team of attackers tries to smash the opposite teams balloons. The team could also decide to let each member carry his own balloon.