On April 26, 1998, approximately 1610 Pacific daylight time, a Piper PA-20 tail wheel aircraft, N7458K, experienced a collapse of one main landing gear leg during the landing roll at Arlington Municipal Airport, Arlington, Washington. The private pilot and his three passengers were not injured, but the aircraft, which was owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 flight, which departed Jefferson County Airport, Port Townsend, Washington, about 30 minutes earlier, was being operated in visual meteorological conditions. No flight plan had been filed, and there was no report of an ELT activation. According to the pilot, he had touched down on both main gear and was beginning the rollout when the left wing picked up and the aircraft began rolling on the right tire only. Soon thereafter, the aircraft started to veer toward the left side of the runway, and the pilot attempted remedial action by applying rudder opposite to the direction the aircraft was drifting. But, by the time of the rudder application, the aircraft had drifted to far from the center of the runway to keep it from departing the runway edge. After the aircraft left the runway, the right main gear dug into the soft terrain, whereupon the gear leg tore away from the fuselage.