Norton by stoppage. Norton was one of those fighters who simply could not handle legitimate HW punchers but was absolutely more than-at-home in fights where he could press and exchange shots with guys who couldn't bother him with single shots. The Ali fight shows that he could handle speed and movement and knew how to cut off the ring. More importantly, breaking Ali's jaw shows us he knew what to do when he had his man against the ropes. Plenty of people have had Roy against the ropes and lacked the brains or size to know what to do. Norton has the know-how and the size to get it done. Norton anytime after the 4th. Just a terrible styles match for Roy, I would expect Roy to do better vs Shavers than against Norton.
