An employee was feeding cardboard sheets into a machine when a jam occurred. He was attempting to unjam the machine when he tripped and used his right hand to catch himself. His right arm/elbow area was then caught between the machine's anvil roller and stop shaft before the machine fully stopped. He suffered a skin detachment injury to his right arm's elbow/bicep area, requiring hospitalization and surgery. The machine was not locked/tagged out at the time of the incident.