On September 4, 2004, at 1320 mountain daylight time, A Piper PA-18-150, N91042, operated by the Nebraska State Patrol, impacted terrain during landing roll on runway 33 (4,800 feet by 60 feet, dry concrete) at Grant Municipal Airport (GGF), Grant, Nebraska. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 public-use flight was not operating on a flight plan. The commercial pilot was injured. The flight originated from Searle Field Airport (OGA), Ogallala, Nebraska, and was en route to GGF. The pilot stated the winds were calm to 360 degrees at three knots. He made a three a wheel landing and after "slowing considerably" the tailwheel contacted the runway. He continued the landing rollout with the first notch of flaps extended and experienced a "gently left drifting movement". He applied right rudder but was unable to correct the drift to the left. He applied more right rudder and felt the back edge of his left boot being pushed against the metal plate attached to the floor where the heel brakes pass through the floor. He pulled his left boot away from the hole and because of the right rudder pressure, he entered the grass on the right side of the runway. Upon entering the grass, the tail rotated clockwise and the airplane slid sideways into a two-foot deep ditch at the north end of the runway. Due to the depth of the ditch, the left main landing gear dropped down allowing the left wing to drop and impact the ground.