This thread pops up every time a Diaz bro scores a knockdown/KO
When will people realise that even though they dont sit on their punches the accumulative effect of having your brain scrambled over and over and over during the course of a few minutes will quickly add up? The left didnt rock McGregor on its own, it was just the first punch where his legs visibly started giving out on him. Diaz had landed repeatedly beforehand, and he continued landing afterwards, rocking McGregor again and then almost finishing him with GnP. Even so McGregor never went out, so I'd say his chin is pretty good.
For reference, watch Nick Diaz vs Paul Daley where a similiar weird looking knockdown occured due to the stockton volume punching.