It's always nice when you get to use a skill you normally don't get a chance to.

I never understood what was happening here and hoped this comic would clear things up. How is Zoro hurting her? He can't be crushing her skull at that angle, his fingers are too obtuse from his palm. He's not suffocating her, with her mouth so open.

Yeah, he's crushing her skull by pure gripping strength. It's a move in professional wrestling to "overpower" the opponent. The iron maiden or something? But, yeah, it's implied that the gripping strength is so over the top that he's squeezing the skull until the person passes out.

The move is called the clawhold, also called the Iron Claw, as popularised by Fritz Von Erich and the Von Erich family

Put your hand on your head, with your thumb and your pinky on either side of your temple. Now squeeze hard.

I get that you're all giving good answers, but look closer at Zoro's pinkie: it's too high according to your description.

Put your hand on your head, with your thumb and your pinky on either side of your temple. Now squeeze hard.
Tried it this way too. Still hurts.

I also always assumed it was the panic of not being able to move him.

Bear in mind that this is a setting where an official author answer confirms that Zoro can speak with a sword in his mouth as it's his heart speaking. If you spot a biological flaw expect the justification to be more insane than just ignoring it.

https://onepiece.fandom.com/wiki/SBS_Volume_5

While crushing her skull is unlikely (though Zoro is strong), there's nerves in your temples and it can be painful when they're pressed for long periods of time.

theres a reason zoro is my favorite straw hat:
PURE
UNADULTERATED
BADASS
from his first appearance getting the nastiest of guitar licks, to fights like this. i dont think anyone else in this universe quite lives up to his badassery. others can have badass moments, but every zoro moment is awesome to an 11. i cant wait to see some of the later feats tbh theres one in particular which is my fave scene in the whole series, but thats WAY down the line

Let me guess: Zoro takes the pain-bubble.