He never had the most iron chin but he was taking big punches and often even very huge punches when hurt prior. That's in a different planet compared to what Prenga dropped him with twice.
This! He has never had an amazing chin but it's totally cracked now and his legs are totally gone before he even starts a round
AJ carries way more muscle mass than someone like DDD. AJ at 251 is still very lean. DDD would have to be around or below 230 lbs to be as lean as AJ is at 250+
For a guy that supposedly has such a weak chin, the man sure can take some shots and keep getting up. That moon shot Dubois hit him with in the 1st round would have sent pretty much everyone in the HW division to dream street. Of course, most guys wouldn't put themselves in a position to be hit by that punch in the first place. I agree with the OP. AJ's chin is basically where it has been his entire career. Average. The real problem is he can't handle himself in the ring anymore and seemingly forgets everything he's ever learned as soon as the bell rings. The very first punch Prenga throws at him in the fight was that big looping right hand that barely ended up missing. What did AJ do as soon as that punch was thrown? He tensed up and CLOSED HIS FREAKING EYES. He acted the exact same way some civilian who gets swung on in their first ever fight does. Then when Prenga steps to him he immediately allows a collar tie, bends over, and never sees that uppercut coming. If you fight that stupidly it doesn't matter how good your chin is. He seemed pretty happy after the fight was over. Acted like he'd cleared a big hurdle and that he has his confidence back. Maybe he does and that means he can be more relaxed the next time he steps in the ring and thus remember basic Boxing 101 stuff like keep your left up and your eyes open. Luckily for him, the only fight he really needs from here on out is with Fury. A guy who isn't as mind****ed but who also looks like warmed over dog****.
That's literally the definition of a glass jaw. Joshua's punch resistance was never great, but now he's clearly packing glass. Anyone who disputes this is just trying to make excuses and rationalize the obvious - Joshua's mandible is shockingly fragile