Ello! This is a grey area so you'll be getting varied responses.
is it legal? should he be able to both use acrobatic AND stealth check in the same move action?
Yes, a player could use stealth and acrobatics in the same move action, but Spring Attack is a Full Round Action that is also considered movement(technicalities, yes, but perhaps important for the discussion).
Spring attack is supposed to be thought of a continuous move with an attack in between. It is unclear (to me) if you can make multiple stealth rolls for a single instance of movement.
Ello! This is a grey area so you'll be getting varied responses.
is it legal? should he be able to both use acrobatic AND stealth check in the same move action?Yes, a player could use stealth and acrobatics in the same move action, but Spring Attack is a Full Round Action that is also considered movement(technicalities, yes, but perhaps important for the discussion).
Spring attack is supposed to be thought of a continuous move with an attack in between. It is unclear (to me) if you can make multiple stealth rolls for a single instance of movement.
well you dont really need to make multiple instances of stealth. Assuming he is already stealthed then he can just move using acrobatics to avoid AoO and then stealth after the attack sequence.
But since both stealth and acrobatics can be done as part of any movement, then the above combo is in fact legal. Just remember that he only get the sneak attack on the first attack when he attacks from stealthed, as the enemy is only caught flat footed on that first attack (has been ruled like this is FAQ). But the combo can be pretty awsome if used correctly.
Be glad that he didnt do the same with a whirlwind fighter though, that is pretty insane. (he just restealths with a 5 foot step after each full attack action.
Given that hide in plain sight can be thwarted by something as common as an everburning torch or dancing lights, I'd not worry about the tactic. Let the player have some fun. :)
Yes, it works. Not sure why he needs to avoid an AoO when he's using Spring Attack, but whatever.
Like the others said, it's not that bad. He's made himself hard to find and hurt, but he's not doing much offensively, either. If his foes don't flee from shadowy areas, they deserve to slowly get picked off, that's his schtick.
(I swear, DMs get more upset about a PC that's hard to threaten than one that can obliterate encounters; it's perplexing...)