The Marquez KO was as bad as they come. It was Hatton, Williams, or Jones Jr. bad. I agree that Pac was looking pretty good prior to that and Marquez was getting busted up and in the previous 2 rounds he was getting pretty mashed facially but then he found the keys to the mansion. The timed punch that potentially ends careers.

People give the example of Duran who came back from a bad KO, but most of the time fighters are not the same. Also, Pac in his next fight will have been out a year and his speed is the key. He is only going to get tagged more and once your brain has experienced being knocked out cold like that, I think it is something that can only deteriorate a fighters resistance. You get tagged hard again and the neurons in the brain start to hyperventilate. The brain probably doesn't enjoy it very much.