On August 12, 2020, about 0800 mountain daylight time, a Stinson 108, N9726K, was substantially damaged when it was involved in an accident near Glenwood Springs, Colorado. The pilot and the flight instructor were uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, upon touchdown, the tailwheel equipped airplane immediately “lurched” right. He said that he tried to correct, and the airplane initially veered left; however, it ultimately veered right followed by a ground loop. The airplane sustained substantial damage to the left wing. The pilot stated that neither occupant was actuating the brakes at the time of the landing. A postaccident examination revealed that the tailwheel locking pin (item #8 in figure 1 below) was sheared, which allowed the tailwheel to rotate freely more than 90°. The locking pin, when properly functioning, locks the steering arm to the tailwheel fork assembly. When the pin is not engaged, the fork has the ability to rotate and pivot independently of the steering arm and rudder input, a condition known as free-castoring. Figure 1: Maule Tailwheel Schematic