Fists are actually not a very good striking device. They weren't meant for it, and it shows in their basic design. The hands are not structured to take a sudden impact against the first two knuckles, and as a result of this, you're more likely to break your hand than you are to do any serious damage.
Therefore, if someone actually moves to punch you in the "traditional" way, then you can use this to your advantage. Such a person is not likely to expect the moves discussed in this node.
SharQ's writeup is good, but a few notes to add:
- In close quarters, elbows and knees are better than fists, particularly if you're right next to the guy. For one, your elbow can take more punishment than your fists, so you can hit harder without worrying about injury. You can substitute elbow blows for punches in any of the methods SharQ mentions, though which one you choose will be more dependent on just where you are in relation to the other person (in front, beside, or behind) and how tall you are relative to the your opponent. Knees are harder to work with, since you will have to be in front of your opponent in order to use them (you do not want to have to turn around to deliver your blow; unnecessary movement wastes valuable time). If you're far enough behind your opponent that you couldn't reach him without turning around, then just forget about hitting him.
- The blow that SharQ mentions is more important than he realizes. You're not trying to knock the guy out flat: all you need to do is stun him for a second or two. Use that opportunity to get away: the important part of a stun-and-run move is run. Luckily, it doesn't take very much to stun someone. A light blow may only get you two or three seconds, but that's all you need.
- As I noted above, fists cannot take very much punishment. So if you are fortunate enough to have a hard object on hand with which you could block the punch -or into which you could deflect the punch, such as a brick wall or car window- then it can be advantageous to do so. If a wall or similar object is directly behind you then you may not even need to block or deflect; simply move out of the way. Depending on just how hard the person was trying to punch you and how strong the object is, this may altogether eliminate the need for a stunning blow on your part. However, this is not very easy to do, so you should not try it unless you are very confident that you will succeed. Also note that trying to block an incoming punch with one of your own, as you may have seen in movies or anime, is a Bad Idea, as your fist is not likely to be significantly stronger than your opponent's.
Finally, if you need to know when someone is going to punch, do not watch their hands. Don't watch their eyes either. Many fighters can use false body language to fake a punch, wait for you to respond, and then react accordingly. A few, as SharQ mentioned, are good enough to catch you by surprise even if you look at these areas. So instead, watch the base of the opponent's neck. You will never face anyone who can feint from here or hide a punch from here.