I am getting sued by my attacker whom I injured while attempting to defend myself against.

I work security for a Hollywood restaurant and witnessed a young man harassing two girls, They asked for help and when I tried to de-fuss the situation he began to harass me and come at me in a threatening manor. I made it obvious that I didn't want a fight, however, when the girls made their escape and he realized, he pushed me and then punched me in the face. He was very intoxicated and after realizing that he was going to really physically harm me I punched him back and knocked him unconscious. The police came and took my statement and when my attacker become conscious again they tried to speak with him and he began to harass them also. They tried to restrain him but could not and had to mace him and put him in handcuffs. He was admitted to the hospital later for head injuries from being knocked unconscious and now he is suing me. What grounds does he have to do this if I was acting out of self-defense and he hit me first?