I once killed a teammate who was stuck in the scenery near our spawn point in a siege match in Mount & Blade: Warband, so that he could respawn and get back to playing the game. Even though it meant taking some damage myself for hitting a teammate, and losing a point for teamkilling.
It was just so sad looking at that guy jerking against a wooden spike, jumping and flailing, trying to get out, and as our team ran past him into the battle, I could see him let out a desperate "help!" every now and then.
He even said thanks.