During the landing roll on a grass strip (runway 9) at a private airport, the airplane encountered wind and began to skid to the left. The pilot turned the airplane in order to level the wings and stop the skid; however, the airplane departed the runway at a 30 degree angle and nosed over in the soft ground. The aft spar in the vertical stabilizer and the rudder hinge were broken. According to the Federal Aviation Administration inspector who examined the airplane, no preaccident mechanical malfunctions or failures were found that would have precluded normal operation. Wind at the time of the accident were recorded as 100 degrees at 6 knots.