EMPLOYEE HAD FINISHED BOLTING #7 ENTRY ON MAINS. AFTER BOLTING FACE HE BACKED OUT OF FACE ABOUT 30' FOR THE BOLTMAN ON OFF-SIDE TO SPOT A BOLT. EMPLOYEE WALKED AROUND TO OFF-SIDE OF BOLTER TO HELP OFF-SIDE BOLTMAN WHEN A LOOSE PIECE OF ROCK FELL FROM A SURFACE CRACK, STRIKING HIM ON THE LEG.