Two employees were installing framing for a 10-foot-by-10-foot overhead door. They had pre-assembled the frame and were hoisting it up with a chain fall. The frame became bound up in the opening. As one of the employees was freeing it from a manlift, the frame was bumped and the choker that was rigged to the chain fall rolled out of the hook on the chain fall, bending the safety latch out. This caused the frame to tip over and strike the other employee. It knocked him down and pinned him to the floor from the left hip to the left shoulder, and he was hospitalized with fractures to ribs on the left side and his left hip.