Instant Wall

[Mathyoo]

Hi,
We played a lot of Munchkin in the past week and encountered a lot of cases where we could not agree on what is legal.

After consulting FAQ and searching online for answers, these questions persist:

4) Instant wall
Can Player A play Instant Wall against Player B who is currently losing the fight, but has not conceeded the defeat yet and intends to play modifiers that will make him win combat. Player A wants to prevent Player B from gaining level 10 and win by "making" him to run from fight.
Here we argued it can only be used after the combat was already lost.

I apologise for bombarding you with questions, alas at least it shows we gave the game a good run! Thank you for your patience, time and help in advance and I wish you all best in 2018!