After watching the fight numerous times, I'm not sure why people are drawing big conclusions either way, because it seems obvious to me that after Joshua was tagged in the third round he had no idea what was going on. Just look at the way Joshua reacted to the second knockdown in the seventh, he wasn't able to respond to simple commands, and look at his interviews, he's completely vacant.
The big mistake that Joshua made was thinking that he had badly hurt Ruiz when he knocked him down, and then he decided to put on a show by opening up and go for the big finish.
Looking at the replays, Ruiz was knocked down because he was caught with his legs square, so he was completely composed when he got back up and was able to catch Joshua with an unbelievably clean shot. I'm not sure of how many boxers can take a clean counter on the temple from a 19 stone heavyweight.
I strongly believe that the ref should have stepped in at the end the fight at the end of the third round, because after the second knockdown then it was obvious Joshua was heavily concussed. I think that Joshua was actually very lucky not to receive a potentially career ending beating, because it seems to me that at times he had no idea about the situation he was in.
So the question is - was this a symptom of bigger boxing issues with Joshua or was he clipped by a lucky punch?
The truth is, irrespective of the strong opinions on both sides of the argument, nobody will know until they have their rematch.