EE was operating an automatic Bemis stacking machine. A filled pallet of cat box filler was exiting the stacker on an exit conveyor. The pallet had a broken board on the bottom. The pallet hung on the conveyor. EE used a pry bar (metal pipe-1 1/4"" pipe 5 1/2') to try to unhang the pallet. As he pulled on the pipe, he felt a sharp pain in his lower back & right leg & hip.