Sequence of Events
Following a landing, a commercial certificated student pilot initiated a turn to back taxi to the departure end of the runway for another takeoff. This was accomplished by advancing the throttle and applying the left brake. As the airplane turned to a position perpendicular to the runway, the instructor assisted the student with depressing the brake because the student was experiencing difficulty.
With the throttle still forward, the instructor released pressure from the brake. At that moment, the airplane's tail began to lift off the ground. The instructor then pulled the throttle to the idle position, but the tail continued to rise. According to the instructor, it appeared that the wind got under the tail and kept it rising. Subsequently, the propeller struck the ground, and the airplane became inverted.