Injured was bolting off side of miner in St Leo 113 blk 3-2 with new section of roof mesh, not bolted to top yet, on the miner when a piece of coal (3'x3'x5"") dislodged, slid down the screen, bounced off the rib and struck EE, resulting in a fracture to the L1 vertebrae. No problems with equipment or compliance issues, training or PPE.