If I have to fight the shooter, how can I defeat them?

First of all, don't fight a shooter if you can avoid it. If you find yourself in a situation where you have to fight a shooter there are a couple of things you can do. If you have a gun, find some cover to hide behind while you prepare to return fire. The priority is not to defeat the shooter, but to stay alive. If you don't have a gun, try to get as close to the person with the gun as possible, with your hands in the air. Then quickly grab the arm that is holding the gun at the wrist, after which you can aim it away from you. Then you can hit the person, do a martial arts technique, etc. Remember, always avoid a shooter.