A team on the rig floor was attempting to rig down a cement head with a manifold assembly from the rig floor down the slide to the ground below. A winch line was being used to lift the cement head off the rig floor to allow the team members to push the head to the slide. The head was pushed out beyond the slide, but the manifold caught on the rig floor and the head swung back toward the floor and struck the swing gate. An employee was holding the swing gate open with his right hand and was struck on the pinky finger. The distal interphalangeal joint was partially amputated.