How is the Sharpshooter injured?

The Sharpshooter finds himself in a pitched battle in a forest with his regiment. The smoke from gunpowder is so thick that he cannot see as he fires at the enemy. The breastworks catch on fire, and the Sharpshooter gets singed. He sees a fellow soldier wounded, and he grabs him and tries to carry him away from the fighting. A Rebel attacks them. The Sharpshooter fights him off. But then a shell explodes. The Sharpshooter is hit in the head with a stone. He falls unconscious.