THE MINER WAS HELPING TO DO A BELT MOVE AND WAS THROWING BELT STRUCTURE NEAR THE BELT TO INSTALL. AFTER RELEASING A PIECE WHILE THROWING THE MINER FELT A PAIN IN HIS BACK. NO HORSE PLAY OR SAFETY VIOLATION WAS THE CAUSE. COMPLIANCE WITH RULES AND REGS NOT A FACTOR. PROTECTIVE ITEMS OR TRAINING NOT A FACTOR.