The version of my team invented was called “balloon ball” and the balloon had to touch a desk, wall, or cubical before it could be hit by a person again. But the important bit is that the balloon wasn’t entirely filled with air, it was partially filled with the propellant from a duster can. That made the “ball’s” path unpredictable.

There was also “balloon ball-ducken” in which there was a 2nd balloon inside the first balloon (and a sometimes a paperclip in the 2nd), but that sport was never quite ready for primetime.