Hagler stops him whilst down on the cards. Nunn makes too many mistakes to get away with this one, but his speed and style give Hagler one of his hardest fights.
Prime Marvin has an extra gear that Nunn doesn't possess, Nunn's a good middleweight but Marvin is a great middleweight. I'm sure Nunn would have some classy moments for the highlight reel before the roof caves in on him.
15 or 12 rounds? Nunn was tricky at his best so it wouldn't be a blowout. Still, you'd have to think Marvin would get to him eventually.