The pilot was conducting a personal flight and elected to land on a grass strip located on a friend’s property. Prior to landing, the pilot performed several low passes to assess the landing area. The pilot stated that the approach and touchdown were normal. During the landing rollt, as he applied brakes, the airplane abruptly yawed right and nosed over, which resulted in substantial damage to the fuselage, lift struts, vertical stabilizer, and rudder. Postaccident examination of the airplane by the pilot and a mechanic revealed that the right wheel was locked, while the left wheel rotated freely. Further examination by the mechanic revealed that cabin floor carpet had migrated upward and was lodged between the right brake master cylinder and the parking brake locking lever, which resulted in the right wheel parking brake being engaged.