I like to think of such sounds as having two general components: a ‘defining’ one, and an ‘impact’ one. The defining one is what sounds up front and tells the listener what the sound is, especially if combined with picture.
The impact one can be anything at all, designed only to pump up the sound to hyper-real. For defining sounds, simply record what things really are: For a face slap for example, record a real slap, hand clap, slap on thigh, etc.
For a body kick, record a fist on chest thud, etc. For impact sounds, anything goes. A broomstick whacked really hard and flat onto a couch or mattress makes a great beefing-up component for a body hit.
Other purely impact sounds: kick drum, fist-pound on closet door (tapered), car door slam (tapered), kicked or stick-hit cardboard box, leather belt snap, whip crack, etc.
In my opinion, especially what I’m loosely calling the “impact” component can and often should be gain-maximized and mixed with the “defining” so that the defining is still the part that gives the information as to what the sound is.
– Clint Bajakian
The tried and true is doing the Rocky – Punching some steak or other large animal part – Dismembering carcasses can be helpful too – though awfully unpleasant.
– Charles Maynes
Try simply clapping or hitting your palm (with varying force – lightly too) close to a mic, add treble and then distort it (try both analogue dist and ordinary digital clipping).
– David Filskov
We stuffed a couple of oven ready chickens with celery, carrots, and nuts, and beat it with a cricket bat. Results were very good. Lots of compression was added to bring down the slap, and bring out the crunch.
– Garry Taylor
For a cheesy, “old-school” punching sound, I had success with:
• Whip a fuzzy blanket in front of a microphone
• Compress the crap out of it until it starts to distort a bit
• Adjust EQ as you see fit. Some high mids did it for us.
If you’re looking for some punching sounds, the appropriately-titled Punch sound effects library offers a good selection.