Witnesses tell us (TMZ) ... the actor got into an argument with another man over a parking spot near 10th Street and 5th Avenue. Our law enforcement sources tell us Alec had a friend holding the spot for him, but the other man swooped in.
We're told Baldwin became irate, an argument ensued, and Baldwin punched the man in the jaw. The alleged victim, a 49-year-old male, was taken to the hospital.
One witness tells us Alec yelled "F**k off" during the fight. Cops were called and Alec was arrested. Baldwin lives in the area.