What would the physical damage be? [Details inside]?

Imagine there is a person held by both arms and in an upright position. What would be the physical damage to the person held if a person other than the two holding him/her took a homerun swing at their head with a baseball bat? Would the damage be worse if it were an aluminum bat? If wood, would the type of wood make a difference? Would a bumper jack be worse than a bat? How would it change if it were a lead pipe, or heavy length of rebar? Would the placement matter, like the nose as oppose to the forehead? What if the person was held facing away and took the blow to the back of the head?