Monzon definitely over 15...more then likely stops Nunn. Over 12 could have been a good fight..Nunn was a very talented and well schooled fighter, his physical size and gifts would have also made it very interesting. I most definitely see Nunn taking some rounds here...but in the end I just cant see him standing up for the whole fight against someone as well rounded as Monzon. For all his talent I think the mental fortitude of Nunn wouldnt be sufficient to take a bloke like Monzon coming at him.
Monzon's physical advantages, and how he applied them, were a large part of his success. He'd be at a disadvantage against Nunn in that regard.
I think at some point, Nunn's bad habits (ie: laying on the inside, leaving his chin exposed) and semi-questionable stamina catch up with him. Monzon by TKO in 11, after a tough fight early.
And in speed, too. I can envision Nunn befuddling Monzon with his quick hands...and slightly longer reach too. I think King Carlos would be in for a long, frustrating night.
