After playing this game (rules are listed here), I decide to find out if we had actually invented it. A google search suggests that nothing quite like it has been played (or at least filmed) before. There are variants of it, including a video of a sumo ring floating on an Olympic size pool, with two women wrestling (not sumo) on top of it, with the idea that one of them was to push the other into the pool. This is not very practical, because Olympic size pools are too big for my budget, and it was intended as a spectator sport.
There was also a computer game called Pool Sumo, but it appears to have only the bouncing aspect of the game, and not the dunking part.
Here are the promised videos, from two best of 5 matches.
In match 1, round 1, Dad (aka “the Beached Whale”) wins the point. A swift, well-placed kick flips Joshua D. aka “the Eel” off of his ring.
In match 1, round 2, Dad wins the point by grappling and pulling Josh off the ring.
When Josh wins a point, it is usually by bouncing me to the edge. (If you or your floatie touches the side you lose the point.) I almost never win a point that way, because he is too quick. But here is a round where we grapple, and I go under first. Maria also shows up as the referee.
If you play this game, we recommend that you wear more than an actual Sumo wrestler.