THE RETAINER PIN THAT HOLDS THE STRIKER PIN IN PLACE ON THE ROCK BREAKER BROKE. EMPLOYEE ATTEMPTED TO MOVE THE APPROXIMATELY 250 LB STRIKER PIN BACK INTO PLACE AND STRAINED HIS BACK. HE SHOULD NOT HAVE ATTEMPTED TO MOVE THIS HEAVY OF AN OBJECT WITHOUT ASSISTANCE. A HOIST SHOULD HAVE BEEN USED. HE IS LOSING TIME AS OF 10/15/03.