Disarms, Trips and conditions in general

If you tell the player they'll get bit if they do something and they do it anyway, they get bit.

Or if that feels too hard, I think it would also be totally legit to say "Cool, you can knock the weapon out of the guy's hand easy, but you're going to leave yourself wide open to the wolf if you do.  Your next move is going to have to be made in the presence of that danger."  Then for their next move they can either Defy Danger or else Defend, but they can't Hack and Slash because they're wide open.

Bob the Fighter - "I roll 7 on that roll to disarm"
Your Loving MC - "Cool, you can knock the weapon out of the guy's hand easy, but that wolf is going to have a clean shot at your ankle if you do. How much do you like your ankle?"
Bob - "Screw it, I knock the jerk's sword away. I'll deal with the wolf late-OW!"
MC - "Yeah, d6 damage doesn't feel that comfortable, does it?"
Bob - "You could've rolled it instead of throwing it at me..."

So, you're actually giving him a hard bargain with the success on what Bob aimed out for on one scale? And a hard move on the.. very same scale where the success is? IMO that's like saying "You rolled 7-9, now pick both 10+ and miss results or neither." And if the player chooses neither, he's really in stagnation, which is not how the rules are supposed to work. Right?

So, you're actually giving him a hard bargain with the success on what Bob aimed out for on one scale? And a hard move on the.. very same scale where the success is? IMO that's like saying "You rolled 7-9, now pick both 10+ and miss results or neither." And if the player chooses neither, he's really in stagnation, which is not how the rules are supposed to work. Right?

I disagree that he's in stagnation. Something happens regardless, depending on what the player says next. Also, I don't feel it's a particularly hard move, so I don't feel its a  miss result. Maybe your misses are nicer than mine, because for my games that's hardly even a consequence. Anyway, essentially it's me turning it into a 7-9 on H&S with alternate damage (the disarming) and a choice to pull back at the last second and do something else, which may or may not trigger a move depending. Anyway, maybe I'd more likely say "You can wrest the sword out of the opponent's hand, but you'll be leaving yourself wide open to the wolf. Otherwise, you can shove the dude away by the sword and leave him with it and focus on the wolf while he get's his bearings. The choice is yours." Maybe not, though, cause I know that my players will leave themselves pretty much every time.

Also what zmook says.

There's no need for stagnation. "I'm not opening myself up to a wolf. There must be a better way. Can I put like a rock outcropping or something between me and that wolf?"
"Well, the wolf is slinking in pretty quick, but yeah. You can get something between you, sounds like a Defy Danger using DEX to me. It should give you a moment to act before it comes around."

Stagnation isnt such a big deal either. Stagnation is just another way to say "Everyone looks at the GM to say something." We know what the GM does then...