Basically, anything that their sporting/entertianment environment outlaws: strikes to the throat, back of the head, breaking fingers, clawing eyes, testicles, etc. Using weapons..
as I think don said, in a no rules environment you can use those "dirty tricks". But so can the other guy. And the person that can do it most effectively and with least risk to exposing themselves to a counter attack is the person with positional dominance...