Board Thread:Versus Battles/@comment-27861278-20181013215759/@comment-27861278-20181015225856

@DMUA I would have to agree that Saitama has some degree of fighting skill, but not to the level that Izzy has, however that's more due to the fact that Izzy has been fighting all his life while Saitama has only been fighting for maybe 5 years max, so in hand-to-hand combat Izzy has the upper hand

However (There's gonna be a lot of howevers in this answer), in character Izzy is not going to fight with intent to kill from the start, especially against a fellow hero, that would go against his Code of Honor, so Saitama might have a chance at the start if he finishes the fight before Izzy takes him seriously.

Another however, Saitama has not displayed his maximum output yet, even his "serious" punch was not everything he could dish out as confirmed by Boros, he still has more power that we haven't seen yet, so he could potentially have an AP advantage. Also, Izzy's Regen isn't going to help him as Saitama seems to have some degree of Regen Null, he displayed this on two seperate occasions: when he met Deep Sea King and when he met Boros, both of which displayed the ability to quickly heal from wounds, but when Saitama punched Deep Sea King, he didn't heal, he just dropped, and when Saitama hit Boros with his Serious Punch, Boros didn't heal, he died. Plus Izzy's regen is only Low-Mid, so if Saitama lands a good hit to Izzy's head, that's it.

Instinctive Reaction might give Izzy an advantage in close combat, however, Izzy's reactions come from his muscle memory, which only triggers when he fights seriously and registers his opponent as a threat, and as I explained before, Izzy is not likely to do that in this situation.