This situation can happen to anyone. If you learn Wing Chun you can cope with it better than someone that doesn't know Wing Chun. - Wong Shun Leung

..... when you punch the head the brain hits the side of the skull.

In boxing, the style has changed over the years from crouching to being more and more vertical. Also people used to jump around, but the modern boxer like Tyson just moves in flat footed to demolish his opponent in a scientific way. In Wing Chun a person does not bob as in boxing. When two beginners fight it doesn't matter how they fight, but against professionals it makes a difference. Even a smaller [person] is better off to keep the body vertical and step back, then to bob and weave. This is because the hand can move faster than the body. Boxing is still like a game because there are rules for how you can hit and how you can't hit. If you attack someone and they bend their head, then in Wing Chun you can still hit them with your hand even without pulling your hand back.

To escape from a rear arm lock, straighten the arm by choosing the best line of force. The hand turns and goes in an upward direction. Then step in and unbalance the opponent.