For Pacqiauo to land a punch, he would need to come within grabbing distance. If he gets grabbed, its game over. So he'd basically have to take him down in one punch.
So the question is, could a 10 stone guy knock out a hard as nails 17 stone of muscle rugby player in one punch?
The answer is no.
I just can't see Manny winning this one I'm afraid. I honestly think I would have a 50:50 chance agaisnt him, if I just rugby tackled him before he managed to punch me I'd win.