HE WAS WORKING ON A D-10 DOZER. HE HAD BOTH PUSH ARMS BLOCKED AND WAS WORKING ON THE OUTSIDE OF THE ROLLER FRAME. THE LEFT SIDE PUSH ARM SLIPPED, ALLOWING THE ROLLER FRAME TO DROP APPROXIMATEL Y 4"". A TRACK CLEAT STRUCK THE EMPLOYEE'S LOWER RIGHT LEG, CAUSING A CONTUSION. HE STARTED MISSING WORK ON 4/29/03.