Fast foot strike down on kneecap or shin, kick to the groin, head strikes such at directly to the tip of nose, eye gouge, all take em out pretty quick. As someone else said you have to know your being attacked and then your primary function should be to strike first and strike to drop them. Leave the body shots as well as the head strikes alone, as in hitting his forhead/skull, as most people won't go down with just a lucky punch.