What kind of defense could be used for my fiancé if he thrown out one person while partying and person left his stuff behind?

A little over a year ago, he and two friends were partying in his home when an altercation between all 3 people happen. He told both to leave. He ended up physically removing the 1 that wouldn't leave. Now he is being charged with theft for the person’s belongings that ended up being left during this altercation. He had no intent on keep them. It’s just that everything was already to the extreme. He wouldn't open the door back up because this person just kept coming back in trying to stay at first, then after being thrown out physically once came back in and attacked him while he was using the restroom. So he threw them back out again locked the door and he went to bed.