According to the police report, obtained by TMZ, Big Sexy and his lady were leaving a restaurant after dinner, when a man approached Nash's wife and began chatting her up.
According to the report, Nash's wife told the guy to buzz off ... but he got aggressive -- so Nash stepped in and dropped him.
Nash held the man down until police arrived -- but in a cruel twist of fate, he ended up getting arrested himself on suspicion of battery, a charge that was eventually dropped due to lack of evidence.
Nash tells TMZ, he never should have been arrested -- and if he wanted to sue, he'd have a good case in court, adding, "I'm a 52-year-old fake fighter. My hands aren't deadly weapons."