Its a good question actually.
When you box for any period of time, especially if you wrap and tape your hands and wear 14oz or 16oz gloves to spar with, it can become deceptive. A number of boxers (including Mike Tyson) have broken their hands in streetfights because they didn't form a full fist and hit with the correct part of the hand (though I'm sure the other guy didn't come off too great either)
If we are talking bare knuckle for SP, then you have major hits and minor hits (to set up the former). Strike with the first two knuckles, usually (for me) with a short right cross, against the tip of the jaw or as close as you can along the jawline, to shake the brain and render the opponent unconscious. The punch doesn't need to travel more than 12 inches and accuracy is far more important than power. That is my major application of boxing tools for a situation outside the ring.
If you need a set up with a minor hit, strike with the middle or outside knuckles to "the button" i.e. the collection of nerves below the nose and just above the mouth. This causes a closing of the eyes, tears, distraction and pain....setting up the main shot to the jaw.
Thats when things go well, but most of the time the fucker usually moves and you hit teeth, cheeks, ears and hair. But thats fun too
