It has directional inputs, a jump button, and two (attack) buttons, and character specific special moves.
I don't really know or have an opinion on weather or not it is a fighting game, but I do love it.
It definitely has some Smash Bros. style movement options. Short jumps, fast falls, wall jumps, dash dancing, etc. So if it's similar to any style of game mechanically, I'd say it's most like a platform fighter.
If anything, it could be considered an unorthodox fighting game (as opposed to traditional fighting game), much like Smash Bros. The grey area comes from how it's entirely based around the ball, making it a hybrid of a sports game (specifically dodgeball).
I'd say that it's "Fighting Game Adjacent"... It has the strategy and metagame of a 2D fighting game, but with the competitiveness of a typical sports game... Regardless, I take every match against Candyman seriously...
Perhaps "combat sport"? Trying to think of other examples of something like that, but I need to leave for work momentarily. I think there's a basketball fighting game from the 32-bit era. Can't remember the name though.