LOADER OPERATOR WAS SCALING THE BENCH. A ROCK FLIPPED OUT OF THE BUCKET, AND CAME THROUGH THE WINDSHIELD. THE ROCK PRESSED ON THE R STEERING JOYSTICK AND CAUSED THE LOADER TO REVERSE DIRECTION AND TURN AT THE SAME TIME THE ROCK WAS PRESSING ON THE OPERATOR'S LEG WHICH CAUSED HIM TO ACCELERATE. OPERATOR STRUCK THE OPPOSITE BENCH. APPEARED TO LOSE CONSCIOUSNESS MISSED 1 DAY OF WORK.