I want to add to the points made by Purespit and Rand86. Unless you have your hands up in a guard etc even a sucker punch from the front is very difficult to deal with. Especially without any telegraphing and if the distance is within range. People who enjoy fighting and violence even when drunk can throw a very fast punch and action always beat reaction. These people have a history of personal violence, the normal emotional brakes are not on, so they don’t need the internal ‘justification for the violence’ process to launch an assault. Consequently martial arts is very limited in what you can do to defend against it. I agree with Robert Map in that don’t waste your time thinking of a strategy to deal with this particular type of assault. Use that time drilling on dealing with a sucker or straight punch to the head using what ever technique you believe is effective against it. As in the final analysis if the no feelings individual want to punch you in the mouth they will do it quick without any hesitation or give off body language leaks of impeding assault. If you are lucky you might have the distance from them to react.