There is already a premise for this one. "Rematch"

A Split Decision or close win are the obvious.
But another obvious one is a controversy brews between Roach and Mayweather (Sr. or Roger) and a DQ happens...perhaps a hit on the break. A stoppage from a cut by a headbutt.

There are a number of possible scenarios that could play out. The temptation is far too great not to make play off any incident to create drama which would make an enormous gate even larger.