EMPLOYEE WAS CHANGING A 6"" BY 84"" BOTTOM ROLLER ON THE #2 NORTH 72"" BOLT. ONE END OF THE ROLLER WAS IN A BRACKET, AND EE HAD POSITIONED HIS RIGHT SHOULDER UNDER THE ROLLER TO LIFT THE OTHER EN D IN PLACE. HE THOUGHT IT WAS SECURED, BUT WHEN HE RELEASED THE ROLLER, IT FELL AGAINST HIS SHOULDER, CAUSING PAIN IN LOWER BACK.