THE ROAD GRADER WAS BEING USED TO SMOOTH OUT SOME QUARRY HAUL ROADS THAT WERE DEEPLY RUTTED DUE TO RAINY WEATHER. THE EQUIPMENT OPERATOR WAS RUNNING THE MACHINE AT 5-7 MPH WHEN THE BLADE HUNG UP ON AN EMBEDDED ROCK CAUSING THE MACHINE TO COME TO A SUDDEN STOP. THE OPERATOR RESTRAINED BY HIS BELT WRECHED FORWARD AND STRAINED HIS LOWER BACK. DID NOT GO TO A DOCTOR UNTIL 11-21-02