Let's say you take a man in good physical condition. He's no Olympic athlete but he's in pretty good shape, pretty strong and fast as humans go. He has some experience in martial arts, he knows what he's doing when it comes to wrestling, boxing and things like that but he's no champion or anything. He has no weapons, no armour more protective than just the every day clothes on his back. What is the strongest land animal that this human could kill in a fight? Of both herbivores and carnivores, what is the biggest, meanest, most physically powerful animal that a human stands a good chance of killing in a face to face fight unarmed?