The odds favor AJ to regain his belts
Yup, one time lost doesn't mean that AJ is done. Considering he didn't get a severe injury, he unlikely to be "punch drunk."
However, as bettor, 2-3x for Ruiz looks pretty tempting in this situation.
Certainly, a single loss does not or should not determine the rest of your fights. But to a lot of fighters there is an indelible psychological effect of their first loss, and for this matter Joshua's American debut as well. This is going to be a very big deal of a fight for Joshua. I am looking at it as his single opportunity to be able to regain the direction of his boxing career.
His loss might mean a boxing career spiraling downAgree with this point
We may want to recall how Lennox Lewis lost to Oliver McCall and Hasim Rahman in his first fights with them. His losses were completely unexpected by KO's (especially with Rahman). So it came as no surprise that he massively overwhelmed them both in the subsequent rematches as the losses made him only stronger
This is not the case with Joshua as he seemed reluctant to continue fighting in the last rounds after the first knockdown by Ruiz (who visibly showed balls after being almost downed himself), and lost more psychologically than physically to his opponent, the meaning being that it may be very difficult for him to recover, psychologically
Technically, he wasn't knocked out but rather surrendered, and it looked like he was no more interested in boxing at all just like Mike Tyson after the loss to Lennox Lewis in 2002 (whatever fights he had afterwards) or even Lennox himself after the elder Klitchko (unlike Tyson, he knew better and retired)
Anthony Joshua is more strong than Andy Ruiz and in this second match Joshna will be hot favorite to win this one. Also the odds suggests the same
He may be stronger as far as physical conditions are concerned, but in boxing it is not all and far from being all. Judging by his fight with Ruiz, Joshua didn't show himself as a tough fighter at all, the Corrie Sanders style (or even the elder Klitchko who proved he could withstand a lot of heavy beating)