EE was posititioned outby the boom of the cont. miner, moving the cable. The cont. miner had completed the left side lift. A piece of rock 4' x 2' x 6"" fell out from between roof bolts. EE saw the rock falling & put his hands up to block it from striking him. It struck his hands, & pushed him backwards. As he fell backward, the rock struck his upper lt leg knocking him down.