Gravball

Gravball is a popular game played by Human children. The game consists of a floating gravity ball, and it is played on repulsor courts. The gravball is "skimmed" across the court, although the mechanics of the game have never been described.

It is a popular activity available on playgrounds. As a child on Eridanus II, John-117 enjoyed gravball so much that they stopped letting him play it because he always won.

Trivia
It is similarly named as Grifball, a gametype for Halo 3 made by Rooster Teeth.