Ok so first we have our commander go out there alone and pretend to surrender. Let's assume they will send just a few men to capture him, and after he kills them they will keep sending men one at a time, just running at him so he can kill one just before another arrives even though they have no reason not to group up and overpower him. Oh and they do also have around 100 archers in a position designed to defend this battlefield, but let's just assume 498/500 shots will miss.

Ok so after that our commander should be wounded and lie down in cover from the archers, now easily killable by a single guy with a long stick right? Let's assume at this point they will send their entire army to stand around him menacingly. This is our time to strike. Let's assume no one in the enemy army thought about why we would send our commander there alone to fight them, while we sneak our entire army there. Thank the Seven no one in this universe has learned to prepare for these sneak attacks even though all battles seem to end in one.

Then we simply run at them and form one of those chaotic messes where we all pair up to fight one of them at a time. As you all know, formations are for sissies. Any questions?