Not so much heroic as it was comical:
My friend was messing around in the Half Life 2 campaign. There was a combine soldier standing against a wall, and my friend was trying to shoot him with the crossbow. Although, at every single shot for about 10 shots, an antlion jumped in front of the combine, saving him from getting pinned against the wall. My friend got fed up and just killed the combine with a grenade.