A crew was preparing to replace a sheave on a spud on a platform barge. The spud was hoisted up with an excavator using a chain rigging so that the sheave could be changed. The injured employee was pulling the cable from the spud hoist drum to provide enough slack in the cable line. When additional cable was released from the hoist drum, the chain rigging around the spud slipped, causing the spud to fall suddenly. The hoist cable quickly tightened and the cable raised off the deck of the barge. The injured employee was then struck by the one-inch, steel cable, resulting in a lower jaw bone fracture.