The pilot was taxiing for takeoff on a crowned grass airstrip which was bordered on both sides by ditches when the airplane started going sideways. The right landing gear went off the side of the airstrip, into a ditch, clipped a fence, and proceeded into an adjacent pasture, rotating 90 degrees to the right before coming to a stop in an upright position. There was substantial damage to the underside of the right elevator, the left elevator and stabilizer, the right aileron, and the right outboard underwing area.