On September 29, 2007, about 0956 Pacific daylight time, a Piper J5A, N38234, descended into a field near the Turlock Municipal Airport, Turlock, California. The airplane was owned and operated by the pilot. Visual meteorological conditions prevailed at the time, and no flight plan had been filed. The airplane was substantially damaged. The private pilot sustained minor injuries during the planned personal flight that was to have been performed under the provisions of 14 CFR Part 91. The pilot reported to the National Transportation Safety Board investigator that he had turned off the fuel selector prior to starting the engine, and he forgot to turn it back on during taxi for takeoff. The engine lost all power and stopped. The airplane was not equipped with a starter. When the pilot hand propped the engine the airplane was not securely tied down, and the throttle was not at idle. The engine started and revved up. The pilot attempted to restrain the airplane by holding onto it, and he sustained injuries in that endeavor. The airplane became airborne with no one inside, and it climbed about 200 feet above the ground. After a few seconds it banked right and descended into a corn field next to the airport.