Getting rid of the referee
If you hit the referee, you can perform illegal moves inside the ring while he's knocked out.
Moreover, the referee leaves the match entirely if you hit him enough times, turning the match into a Brawl.
If the referee is hit enough to leave the match and you're fast enough to hit him outside as he leaves, he will come back and serve as an enforcer/outside referee. Once done, the only way to win is via a submission or a countout (although the latter can crash the game).