General has heart attack mid battle.

[Es Arkajae]

Or he could even have it during the middle of the pre-battle speech.

"Now when I come before you and say 'this' is my kind of fi-urk-arghhhhh-ooohhhhhhh-ackkkkk-arghhhhh"


*Falls off his horse dead, stunned army stops cheering*



In the absolute silnece afterwards someone drops a pin, this startles the Eastern infantry who promptly run away.