This is from p 276 of Apocalypse World, under the heading "playing with the form":
The need for the GM to be able to reimagine things is particularly relevant to thinking about the balance between the agency of different participants in relation to the fiction.
Here’s a pretty interesting custom peripheral move:
This is for times when the player springs things on you in the moment, like “say Rolfball, see that red dot on your chest? That’s the sniper I brought with me” or “oh, of course I gassed the beast up before we left Hatchet City.” This move lets you as MC go with it, but without always giving the player her way. Sometimes you have to say “wow, so you did! A sniper!” but other times you get to say “yeah, about that? You’ve been waiting for that dot to appear, but it hasn’t yet. What do you do?”
It’s not nuts to have a move follow what’s happening at the table in the real world, not what’s happening in the characters’ fictional world, like this one does. After all, a hardholder’s wealth move — “at the beginning of the session” — does the same, with no problems. I will note though that this move in particular changes the creative dynamic of the game. It’s small but fundamental. It means that the players have to be a little less careful what they launch their characters into, and you as MC have to be a little more willing to reimagine situations as you go. It’s not for everyone’s Apocalypse World.
When you declare retroactively that you’ve already set something up, roll+sharp. On a 10+, it’s just as you say. On a 7–9, you set it up, yes, but here at the crucial moment the MC can introduce some hitch or delay. On a miss, you set it up, yes, but since then things you don’t know about have seriously changed.
This is for times when the player springs things on you in the moment, like “say Rolfball, see that red dot on your chest? That’s the sniper I brought with me” or “oh, of course I gassed the beast up before we left Hatchet City.” This move lets you as MC go with it, but without always giving the player her way. Sometimes you have to say “wow, so you did! A sniper!” but other times you get to say “yeah, about that? You’ve been waiting for that dot to appear, but it hasn’t yet. What do you do?”
It’s not nuts to have a move follow what’s happening at the table in the real world, not what’s happening in the characters’ fictional world, like this one does. After all, a hardholder’s wealth move — “at the beginning of the session” — does the same, with no problems. I will note though that this move in particular changes the creative dynamic of the game. It’s small but fundamental. It means that the players have to be a little less careful what they launch their characters into, and you as MC have to be a little more willing to reimagine situations as you go. It’s not for everyone’s Apocalypse World.
The need for the GM to be able to reimagine things is particularly relevant to thinking about the balance between the agency of different participants in relation to the fiction.