How many muscles does it take to punch somebody?

Answer 1

Theoretically, as few as just one. Extend your arm with your tricep and your hand flops forward into your opponent's face. Mission accomplished.

For an actual punch as hard as you can with good form, all muscles in your hand, your forearm to twist your wrist, tricep to extend your arm out all the way, Bicep to bring it back to guard, all areas of the deltoid, and a little bit of you pecs where the tendon connects to the front of the deltoid, Also your lats to keep your arm up and lats for full extension, because the are connected to traps, and deltoid, your abdominal and obliques to twist your body with the punch for more power, and also your hip flexors, all leg muscles (whether you twist rear leg or not for power) to keep you standing and balance after the punch so you don't fall over.