Defy danger is quite clear, but unless everyone is looking at the GM or there exists a golden opportunity, does the GM get to make a (soft) move with every partial success? For example, volley 7-9, player decides to lose 1 ammo. Should the GM also make a move? Is the "lose ammo" considered the GM's move in this case?
"That's my secret, Cap. I'm always making a move."
So, let's lay some groundwork here: (The GM is "you", even if "you", the asker, aren't the GM.)
Should you go above and beyond the call of duty to drop some pain on Fletcher on a 7-9, even when the move doesn't say so or he picks a choice that doesn't say so, e.g. place himself in danger to get the shot? NO.
Should you make a move within and fitting the call of duty in response to the results of Fletcher's move, even if he gets a 10+? YES. DEFINITELY. ABSOLUTELY.
Right, so what's the difference? Well, it's down to the difference in the circumstances of the GM and the players.
Move (Player) != Move (GM)
Later hacks have actually renamed the things the GM and GM-controlled actors like locations and monsters do from "moves" to things like "cuts" or "reactions", to distinguish them from player moves.
In terms of their standing as participants in the conversation of the game, a move does the same thing for both the player and the GM - it wraps their part of the conversation and puts the focus on the other party. But while the players represent a united front (or at least a coherent one) a GM is expected to represent the entirety of the world, not all of which is trying to murder the players right now.
So, most player moves are there to present the chance the GM will have to give up something - information, hope that a lobbed alchemist's grenade will do damage, the right for Warlord Kithrak to keep drawing breath. But GM moves aren't there to take things from the players as much as they are to get some kind of response from the players. They can draw the players toward good things, push them away from bad things, hand them consequences to deal with, give them rewards they've earned, or just present a meaningful choice to be made.
You have several responsibilities as a GM; you will be called on to describe the situation and exploit your prep. But whenever you expect the PCs to take action, you should frame their action by making a move.
When you're in a featureless white room on the Internet it's a little bit tough to talk about what kind of moves you'd make as a GM and how you'd make them, so how about we go somewhere else?
When does everyone look at you?
Right, here's the situation. Fightgar and Fletcher are crawling through an earthen tunnel. The trees of the Whitewood Forest have been animating and assaulting caravans, and they found the twisted tree at the center of it all and the gaping hole underneath its roots. At the end of the tunnel is an underground grotto with a vile shrine in it, angry violet roots wrapped around it, and a wild-eyed gnome dressed in rags and reclining on a pile of furs. Fightgar demands some answers from him, but he dances a laughing jig and fades away, leaving only the laughing behind.
Then the pile of furs roars and lunges at Fightgar, because it was actually a giant mutant badger.
You know, pretty standard stuff. Fightgar and the mutant badger mix it up for a bit, and:
Fletcher: Right, while Fightgar's got it occupied, I nock an arrow and draw a bead on the badger. Just a Volley here, straight up? I don't have to worry about firing into melee?
GM: Just a Volley, yeah. Hit it and you won't have to worry about firing into melee. Are you sending Rockjaw in to help?
Fletcher: Nah, we don't know where the gnome went. Rockjaw's hanging back with me. +dex gives me... :clatter: 8. Hm. Well, I brought these arrows for a reason, I'll mark off 1 ammo and do full damage?
GM: Sure. Under all that fur you're not sure what's a weak spot and what's an oozing, bony plate, so you just keep firing. What's your damage?
Fletcher: :clatter: Oh, big 6!
Okay! So: who at the table knows what happens when the giant mutant badger takes 6 damage? Fletcher? Fightgar? Nope, it's just me, the GM. Everyone is looking at me to find out what happens.
You might think: but wait, that's really simple, isn't it? That's baby stuff. You're going to make a move because they don't know if the badger's dead yet?
If you're thinking that way, you're still thinking of a move as something bad I the GM am doing to the PCs, and it's not. A move is something I present to the PCs to get a response, and I should make a move that follows. Fletcher didn't choose to put himself in danger, or roll a miss, which would entitle me to turn up the danger however much I wanted. But this is already kind of a dangerous place, with the vile shrine and the angry roots and the pool of unknown provenance and the invisible mad gnome. So I'll put someone in a spot and offer an opportunity.
GM: Right. The badger cries out and lists to one side, but that doesn't stop you from putting arrow after arrow into it. As you're drawing the last few of that ammosworth, you hear a loud cry from off to your right-
GM: -and hey! Fightgar! So Fletcher turned the badger into a dang pincushion, and its mass falls directionless onto you. A little exertion is enough to brush it aside, and you turn back to Fletcher but hear a loud cry from off to your left. Man, it's been a while since you heard Groundtongue, and this has got a bit of gibbering in it, but you're pretty sure it was "No! My badger!" The gnome's glamer shatters, and hoo boy that's a big knife he found and he does not look pleased with Fletcher at all. So tell me, are you going to run back and protect Fletcher, or let him and Rockjaw deal with the gnome while you, say, do something about that shrine?
To be clear here, Fletcher's not in, like, mortal peril. If Fightgar goes to mess with the shrine or whatever, well, Fletcher's got his bow out and there's a gnome closing to knife range at the speed of madness. This is a downside of Fletcher's gear that he'll need to work around somehow, but it's not some special unfortunate event; it's just the next thing that's happening in the battle. It'd be happening even if Fletcher rolled a 10 and didn't pick any downside at all. Comparatively, rolling 8 and picking to be in danger would be something like "a gnome is on top of you and about to stab you". Missing the roll would be "a gnome is on top of you and has already stabbed you some", or if I'm feeling saucy, a choice between "you snap off a few careless shots and split your damage between Fightgar and the badger" and "you take too long to aim and a gnome is on top of you and has already stabbed you some".
In any case, now Fletcher and/or Fightgar have something to respond to when I turn the conversation to them and ask what they want to do next.
Picking what you do to the PCs in a dangerous situation - whether you make a threat, raise the stakes, or go for the throat - is admittedly more of an art than a prescribed response, and developing that judgement is part of becoming a good Dungeon World GM. If things get dire enough, PCs can find themselves suffering terrible fates even on a clean success, but if things have gotten to that point, you should tell the PCs the requirements or consequences of sticking around.
Finally, there are some situations where a PC makes a move and they're not looking at you to tell them what happens next. For example, Fightgar and Fletcher might explicitly set up with you some kind of a two-part scenario where, say, Fletcher fires distracting shots at the water weird while Fightgar scrambles back to grab the shrine's keystone. In those cases, you can resolve Fletcher's move (which is probably some kind of aid roll) and then immediately snap over to Fightgar to carry the results forward.
But in general, when PCs make a move, they're tossing dice into the unknown and looking to you to tell them what happens next. So give them something to react to. Make a move.
No, a GM move is only triggered by a miss or being looked at with that “what happens next?” look. And the rule for moves is that they do only what they say to do.
So for player moves, only a miss results in a GM move, and on a hit (including the 7–9 hit) you do only what the move says to do.
For a 7–9 hit on a Volley, the player follows the move’s instructions. If they choose “lose ammo”, that’s what happens. It doesn’t count as a GM move.