The pilot and two passengers planned on a local flight. The beginning of the takeoff roll was normal, with light winds down the runway. According to the pilot, when the airplane reached about 60-65 knots, the right seat passenger inadvertently pushed on the left rudder pedal. The pilot was unable to stop the turn; the airplane departed the runway surface and proceeded down a grass embankment. Examination of the airplane revealed substantial damage to the outboard section of the left wing and aileron. The pilot did not report any mechanical anomalies that would have precluded normal operation.