Here's what I think happened.I think Bellew, Froch etc were spot on.
AJ just didn't have that 'fear factor', did he underestimate him? Only he knows. Fair fucks to Ruiz though, can tell what it means.
Reckon AJ will do him at Wembley personally, but who knows.
Because the fight was made at short notice, AJ's camp hadn't had the time to do their full research and relevant training. On top of that, he almost certainly was getting cocky and probably didn't take things seriously enough.
When he got that first knockdown, the first time Ruiz had been knocked down in his career, he made a mistake. First of all, he couldn't be too sure whether he'd hurt him or just caught him off balance. Secondly, not being prepared enough for Ruiz specifically, he should have said to himself, 'I have 10 and a half more rounds, just keep doing what I'm doing and I'll win easily'.
Instead, maybe with the pressure of this being a showpiece fight and with Wilder's recent 1st round KO, he decided to come inside and go for the kill. Against a shorter height, shorter reach, lightning handspeed guy with a 20st power base who he didn't know much about and whether he was truly hurt. Lo and behold, Ruiz catches him with a great counter, wobbles him and takes him down.
Personally, that first knockdown was brutal enough to set things going against him. He was up against it from there and the damage was done. And the fact he wasn't prepared for how to deal with a guy like Ruiz just made his life really difficult. And the rest was history.
What's disappointing is that in the end Ruiz didn't have to box smart. Joshua just boxed like an idiot.