Usually a one on one fight where anything goes you can use any type of fighting style whether it is a martial art or just plain boxing and wrestling. You can use knives,samurai swords,bats,beer bottles,etc anything you can get your hands on. The fight usually ends if someone dies,gives up or just passes out.
One of my buddies was in a street fight and kicked the guys ass. He slapped the guys hat off and then when the guy tryed to pick it up, my buddy kicked him rite in the face knocking him out in one blow.