Punched a cop in the face and knocked it out cold?

Last weekend I punched a cop in the face and knocked it out cold. This is how it happened. It verbally aulted my girlfriend during a traffic stop as we were outside of the car. (he made us get out for arguing the validity of the stop with him) We were totally calm and respectful but it didn't like that we were questioning the legality of the stop. It started screaming in my girlfriends face and made a sudden movement towards her and pointed it's finger in her face. I was afraid for her safety so I pushed it. Then it said "oh you wanna go" and pulled out it's baton. When it did this I punched it face (haymaker, all I had) and knocked it out cold. Then we left. My girlfriend was freaking out so I turned myself in. I posted bail. I have a few questions. First, I have no criminal record. I served in Iraq during the surge and have never gotten in any trouble in my life at all. This cop was a complete psycho and I was honestly scared he was going to hurt her. How much trouble am I in?