Worker was using a jackleg to bolt the back in 2700-400 Mud Pond. A piece of rock about the size of a softball dislodged from the screen on the back that fell approx. 15' striking EE's hard hat and then the bridge of EE's nose. The rock caused a laceration to the bridge of EE's nose. The miner received 5 stitches and was released to work with no restrictions.