Why does Henry envy the other soldiers? How does he become wounded? What is ironic, or contradictory, about his "red badge"?

Henry wishes that he had a red badge of courage (a wound) like many of the other more seasoned soldiers. He sees the injured soldiers around him and wishes he had something to show from battle. Henry becomes wounded when he stops a fleeing soldier. The soldier (on his own side) hits him in the head with the butt of his rifle. The irony is that Henry didn't get his "badge" in battle but from a fellow soldier running away in terror.