An interesting concept.
Let's star by saying, that the main idea of leaping at your opponent, in order to push them out of the bounds of the ring, fits the theme perfectly! It is also fun to play in it's current state, and if you'd work on it a bit more, that could become really something! Unfortunately, for now, the game is a bit too easy, even on the hard level.
The graphics are okay. I liked the models of the sumo wrestlers. They look funny, their animations are funnier, and in general, I like the minimalistic approach to this game!
However, I don't like the minimalistic approach to the sound effects. There are only three sound effects total in this game, THREE. That makes the game feel empty, and, no offense, but I found the voices really irritating.
This is a really simple game, with an idea that has potential, and that is fun to play! Should you continue the development, and add some polish and balancing changes, this could be a really good game!