Judd, my interpretation in that case, when what you want them to do (die/bleed) is the same as what you want from them (life/pain), is like so:
If they're not immediately ready to fight back, if there's any way you can catch them off guard, then it's going aggro. It's harder to hurt them in this case, since on a 7-9 they can probably dodge out of the way. Or maybe they suck it up and spit a tooth at you, MC's call. This move is good for "I pop out of cover and ..." kind of moves.
If they're all just you try and throw a punch at me, fucker, then it's seizing by force. You're like, "that's it, I raise my fists and charge at him." It's easier to do harm for certain, but even if it's just a fist fight, more likely that you'll get hurt yourself.
It's a good opportunity to reinforce the "damnit, describe shit for me" thing, where if they want it to be going aggro, they need to dish out the fiction so you all can go, yeah, that's totally what it is.