You did not say how old your son is. That will affect how you will approach this problem. He needs to understand that fighting is not an acceptable way to solve problems. He needs to learn how to solve disagreements without fighting. I try to find a logical consequence for misbehavior. If that is not possible, find something meaningful that you can take away (such as his cell phone or video game time). He needs to understand what is expected of him in order to regain his privileges.