He is fighting an enemy that has all to lose, and nothing to save. A fact that he seemed to be aware the moment Ansom scr... sent him.
In a situation like that, you have to expect everything, as it's quite obvious to everyone knowing the Erfworld art of war, that ALL Gobwin Knob troops are defending the only menaced area (underground).
Guess who is guilty? Name the one over chief that ordered to delay the wall assault.