Thanks for the replies, everyone. :-)
Yeah, I get that we could "just" resolve everything in the fiction. In the same way, we could "just" resolve fight scenes, or parleys, or whatever, in the fiction, too, without ever making recourse to the dice. However, the dice are there to add excitement, tension, or unexpected results to a situation.
Now, I wouldn't call a chase a mere mechanical generality; they're a dramatic staple of fiction of all types, and rightly so; they're exciting, dramatic, cinematic. So, without adding lots of distracting deviations from the core element, I'm trying to consider a way a PC could stop an NPC from running away, catch them up, etc. The mirror of Defy Danger.
I guess in a sense there's a top-level, unnamed "Stop the NPC!" type move "above" moves like Hack & Slash and Volley, both of which aim to 'stop' an NPC using STR or DEX. You could certainly use Volley to stop the fleeing orcs in my example. So perhaps my "Stop them Orcs!" is an instance of this; I could likewise imagine doing a kind of "Stop the NPC" Move using INT to represent fast talking an NPC into silence, using CHA to represent winning an NPC's favour (not simply Parley), and so on. I'd use STR to wrestle an opponent to the ground (one possible option for the chase sequence, depending on the narration), DEX to run and tackle someone, even CON if it was a long-distance chase where endurance, etc, was a factor.
For results, I'd probably go with:
10+ : you achieve your goal, stopping the NPC
7-9 : you're making progress, or you achieve your goal, but at cost (soft move, such as you attract attention, drop some gear, incur a -1 forward, etc). This implies, like Volley and Hack & Slash, that the move may be repeated, narrative depending - that's kind of nice, as it plays to the attritional nature of chases without being overwhelming. There may also be some mileage in putting some choices in here, as with Volley.
6- : your quarry eludes you, or you catch them but they attack (narrative depending, probably a hard move)
I'm thinking that kind of "Stop the NPC" notional move might easily translate into improvised moves like "Pursue", "Debate", etc. Like I say, kind of like Volley or even Hack & Slash, but without the HP damage. :)
EDIT: thinking about this some more, I guess the "Stop the NPC!"-type move is actually a version of the Aid / Interfere move, but where the target is an NPC rather than another PC. It might be interesting to tackle it like that, especially as it implies there's also an "Aid the NPC!" side to it, too. :)
Cheers,
Sarah