The pilot stated that he had completed four landings, and while at a fast taxi he touched both toe brakes. The airplane began a gradual turn to the right. He corrected the right turn first with left rudder control then left brake, however, neither action corrected the tightening right-hand turn. When the airplane encountered the edge of the runway, it nosed down and tilted to the left, substantially damaging the left wing. The pilot described the right brake as "dragging" throughout the accident sequence.