Sports games does not usually have story, but story is, that Dr. Eggman opened basketball field, where anyone can enter for competition.
Soon after opening, Dr. Eggman turned the playfield to monster field, filled with monsters!
But it's all up to Sonic the hedgehog to stop the mess!
Even I also confirm some Pokémons to appear in the game, but if I do, then those appears in background!
But who cares, if I have no lots of ideas to make story!