What error? What result?

Cassius is upset because he is afraid his men are running away from the field of battle. He tells Titinius that he personally killed his standard-bearer who was trying to run away and took up the banner himself. Titinius informs him that Brutus "gave the word too early" (5.3.5) and that his soldiers quickly started looting the enemy camp once they captured it. In the meantime, Antony's army has been able to surround Cassius.