Using these codes on the screen with three basketballs in versus mode will create the desired effect. You will have to use the Square/Triangle/Circle buttons to input them.

1 2 3 Alternate Outfit
1 3 4 Big Head Mode
2 1 3 Speedy Players
4 3 3 Tiny Ballers
0 1 1 Tournament Mode

Unlock all players

Simply complete Story Mode once to unlock all the hidden ballers.