A belt ripped on an 8x20 screen causing mud to fall through and build up on the tail Polly stopping the conveyor. LOTO was performed. EE started chipping mud off the Polly using a 30-inch pry bar to knock the mud away. EE used EE's right hand to brace self against the frame of the belt and used EE's left to chip. As EE was chipping, EE missed the Polly and hit EE's right thumb.