On May 21, 1998, at 0730 central daylight time, a Grumman G-164A, N9632, operated by NOCO Ag Service nosed over following a loss of directional control while landing on runway 15 at the Red Lake Falls Municipal Airport, Red Lake Falls, Minnesota. Visual meteorological conditions prevailed and no flight plan was filed. The commercial pilot was not injured. The airplane was substantially damaged. The 14 CFR Part 137 flight originated from Red Lake Falls, at 0700 cdt. The pilot stated she made a three point landing on the grass runway. She stated the airplane rolled for about 100 feet, then the rollout was continued on the paved runway. According to the pilot after traveling about 50 feet on the paved runway the airplane turned to the right at a 10 to 15 degree angle from the centerline. The pilot stated she applied full left rudder followed by the left brake. The airplane veered off the paved runway surface where the pilot applied both brakes. She stated the airplane skidded for approximately 75 feet prior to entering a plowed field where it nosed over. The runway dimensions at the Red Lake Falls Airport is 2,550 feet long and 148 feet wide. Near the approach end of runway 15 there is a section of the runway 1,000 feet long by 60 feet wide which is paved. Inspection of the airplane was conducted by an inspector from the Federal Aviation Administration Minneapolis, Minnesota, Flight Standards District Office. The inspector reported that skid marks were visible on the runway which indicated the right wheel was locked up. Inspection of the wheel failed to reveal the reason for it locking up.