According to the pilot in the high performance, tailwheel-equipped airplane, he accomplished a normal wheel landing, to the asphalt runway, in light and variable wind conditions. He reported that during the landing roll, the tailwheel settled to the runway and began a "violent shimmy". The airplane exited the left side of the runway and ground looped to the left. The right wing and the elevator struck the ground. The pilot taxied the airplane to parking. The airplane sustained substantial damage to the right-wing and the elevator. Shortly after the accident, the pilot retrieved a metal clamp from the airport, which he believed was on the runway during the time of the accident. The accident airplane was originally manufactured with tricycle landing gear and was converted to a tailwheel-equipped airplane. A Federal Aviation Administration, Aviation Safety Inspector examined the airplane's tailwheel assembly to include the tire and the wheel. The Inspector reported that he inspected the tailwheel for any signs of a clamp getting caught in the tailwheel assembly. He reported that there were no signs of any scarring to the wheel or the tire, or the steering assembly. There were no signs of tire damage from skidding and the control cables for the tailwheel were intact. He reported that, "there [was] no visible sign of any sort [that] this tailwheel was operated any way other than what it is designed for, and there is not any physical sign it was ever not following the [input's] from the pilot".