A lot of the stuff in this thread it
far too high-minded. Are we seriously having a discussion on the relative merits and biomechanics of the vertical fist punch? That is
not the sort of thing you should be mulling over when a fight actually breaks out and you are
actually being hit.
The simple fact is, if push comes to shove (and shove comes to blow) and you're asking yourself whether or not the next punch you throw might hurt your hand you're in totally the wrong place mentally and will probably take a beating. You're also dreaming if you think a scrap with some idiot on a night club dance floor will involve anything more than the briefest flurry of punches before said idiot tries to tackle you or throw you in a headlock. (Also bear in mind these things seldom last even one minute.)
My advice therefore is get yourself a good Thai clinch to keep from being rushed down, crouch with your head low and throw knees to the side/ribs or solar plexus. (If you feel you can get the face though, by all means, go for it. Few things stop a guy in his tracks faster in a "real" fight than being smashed in the nose.) You'll find yourself at an advantage because most thug tough guys will try to keep their heads up and be maintaining eye contact with you or at least staying so they're looking
down on your head - instinct, despite the fact it doesn't really make sense - and are fixated on punching you in the face and will not think to use their knees themselves.
One of two things will happen, probably. They'll try to jerk back out of the clinch so they can throw their haymakers, in which case momentum is on your side; press ahead. (The Burmese boxer's
clinching headbutt is your friend - skip to 4:55. Note he does not "whip" his head forward though!) If not that they'll really try to bull forward to close the distance chest-to-chest and put you on your back/throw you in a headlock. If your clinch game is decent you should be able to stop this, but if the guy is very strong or bigger than you are it might be a problem. Shovel hooks (preferably to the liver) are the order of the day here - proably he will still insist on swinging for your face - but for God's sake learn to sprawl so he doesn't end up on top of you if he
can carry you to the floor.
A final tip (observation, really) would be to keep in mind that it can be quite easy to break collar bones punching bare-knuckle, and that it's much easier (and safer, I guess) to land a solid shot on one than on someone's chin or nose if you really are scared to aim shots at anything on the skull. In the main, though, don't waste time over-analysing optimum "targets" mid-brawl or you'll be repeatedly clocked by the guy who just swings wildly.