On February 17, 2007, about 1350 Pacific standard time, a Luscombe 8A, N515SF, owned and operated by the pilot, veered off runway 7R during landing rollout at the Compton Airport, Compton, California. The airplane impacted a parked and unoccupied airplane and then came to rest upon impacting a wall, on the north side of runway 7L. The airplane was substantially damaged. The private pilot and passenger received minor injuries. Visual meteorological conditions prevailed at the time of the personal flight, and no flight plan had been filed. The flight was performed under the provisions of 14 CFR Part 91, and it originated from Compton about 1315. The pilot reported to the National Transportation Safety Board investigator that he allowed the passenger, who was not a current pilot, to land the airplane, but that he was "following" him on the flight controls. The passenger did not remove his feet from the rudder pedals during landing rollout, despite the pilot's repeated requests. The airport manager verbally reported to the Safety Board investigator that he observed evidence of a "medium intensity" tire skid mark on the runway's asphalt surface commencing about 600 feet upwind of the runway's threshold. The mark corresponded with the airplane's right main landing gear tire. There was no evidence of a corresponding rubber transfer mark onto the asphalt from the left main landing gear tire. The rubber transfer mark from the right main tire became "heavy" by the time the airplane had crossed over runway 7L and was veering toward the parked airplane, located about 130 feet north of runway 7L's north edge. The pilot stated to the Safety Board investigator that no mechanical malfunction or failure occurred during the landing. He indicated that airplane control was lost because of the passenger's interference with his application of pressure to the rudder pedals.