The airplane was parked on the ramp next to a hangar as the pilot attempted to start the engine with the help of two others. The engine was difficult to start, so the pilot exited the airplane and elected to hand prop the engine. Witnesses stated that the engine started suddenly and unexpectedly. The airplane turned right away from the hangar and taxied quickly. The pilot, who was in front of the left wing, ran toward the cockpit door and attempted to climb into the airplane. The pilot fell off the wing and sustained serious injuries. The unoccupied airplane continued across a taxiway, briefly became airborne over the runway, then settled onto the grass and impacted the airport perimeter fence. The airplane sustained substantial damage to the fuselage and both wings. Due to the pilot’s injuries, he was unable to provide a statement for the investigation. Multiple attempts to verify the magneto switch position were unsuccessful. The position of the magneto switch at the time of the accident could not be determined.