Some if my friends of mine got a game going that went pretty well. Gets a pretty good rush of endorphins going. Nothing quite like trying to take out a guy who's got about 30lbs of muscle on you, only to be swatted away. Or getting tackled hard/fast enough that you roll on your back and your weight is balanced between the back of your head and neck, while you can kick the ground over your head. Or getting your jaw messed with so that it's now misaligned and won't fully close on one side without a gap that shouldn't exist.
But it was all in good fun.