What an odd ending.
After referee Joel Cortez temporarily stopped the fight and separated the two fighters due to a clearly illegal head butt from Victory Ortiz, he deducted a point from Ortiz. He then re-started the fight. After exchanging a huge to demonstrate good will, Mayweather landed two punches to a totally defenseless Ortiz that sent him crashing to the canvas.
The problem for Ortiz is that what Mayweather did was totally legal. Here's Brent Brookhouse's take on it:
In the fourth round, one of the oddest moments in recent history went down. Ortiz trapped Floyd against the ropes, was landing to the head and body and suddenly threw a completely intentional headbutt. Referee Joe Cortez broke the fighters up and deducted a point from Ortiz.
Victor walked up to Floyd, apologizing for the clearly intentional move. The two men touched gloves but Ortiz tried to take it a step further and hug Floyd. Instead of an embrace, Mayweather threw two very hard shots knocking Ortiz down. Cortez clearly had not restarted the bout and was talking to the judges.
Instead of sorting the issue out in the moment, Cortez counted Ortiz out and awarded the knockout win to Mayweather.
It was a very hectic and confusing situation but the replays made it extremely clear that Cortez had not yet signaled for the fighters to resume fighting.
From my vantage point, Cortez did start the two back together, but then didn't pay attention giving Ortiz the impression the fight had not been properly restarted.
To make mattes more surreal, Mayweather took umbrage at Larry Merchant's suggestion his actions were either illegal or unsportsmanlike or both. Merchant eventually told Mayweather if he was 50 years younger he'd try to 'kick [his] ass'.