To be fair, Ruiz caught him when Joshua was trying to finish him. I don't think he recovered from that punch.
Er. You mean how do I know aside from me being a once feared street fighter and a gypsy bare knuckle warrior? Khan actually had a very solid chin prior to getting cracked with that savage clenbuterol bomb from hell from a 190lb Clenelo
He doesn't have good instinct when hurt .when he got stopped in the amateurs by that Romanian he looked clueless rather than concussed.he is the same now .I expect him to be KOED in the near future and retire if he is sensible.
I think AJ has a pretty good chin. He got up against Klitschko and took some hard shots. Took Whytes left hook Took some good shots against Parker. Got up all 4 times against Ruiz And in my opinion was more off balance than hurt against Povetkin. He certainly ain't got the best chin in the division, but I feel his chin has become underrated since his loss to Ruiz