AT BOTTOM OF SUPPLY SLOPE ON MAIN LINE TRACK. MAN WAS REMOVING A SKID OFF TRACK RAIL THAT WAS BETWEEN A SUPPLY CAR AND A DOLLY. THE SUPPLY CAR COUPLER SLIPPED OVER THE EDGE OF THE DOLLY-CAUSIN G CARS TO COME TOGETHER. MAN'S RIGHT ARM WAS PINCHED BETWEEN DOLLY AND SUPPLY CAR.