What should you do to win a fight against a big guy?

Kick them straight in the nuts. That puts any man down !

Yes, a swift kick in the nuts works, but it also depends on the circumstance. If you are truly afraid for your life, punch them in the throat (not with a fist, with your knuckles curled on you fingers), if it is a simple schoolyard fight DON'T DO IT ! It can be a fatal shot. Use your smaller size to out speed your opponent. Stay out of range, if he out weights you, he is stronger. Good luck