Considering the UFC rules, I would have to give it to Rousey if Mayweather was not able to take control of the ring and avoid Rousey's grappling skills. If Rousey was able to get clinched up, the use of knees and elbows (which she has more experience at) would be to her advantage, as well as her ability to place opponents in arm bars from virtually any position. If Mayweather was able to maintain distance and movement I think his extensive skill with striking would end the fight in his favor.
Basically, it would depend on who was able to take control of the fight and maintain their advantage based on their personal skill set.
You can't escape grapple without grapple. Rouesy could probably take him out with a trow. He has a strikers chance. Rhonda has a soiled advantage.
ronda rouse i would have to say she is pretty darn tough
cris cyborg.
In a UFC style fight
