On August 10, 2014, at 1000 central daylight time, an Aeronca S11AC, N4240E, veered off the runway and impacted trees during landing roll on runway 5 (3,170 feet by 165 feet, turf) at Boulder Junction Payzer Airport (BDJ), Boulder Junction, Wisconsin. The pilot sustained serious injuries. The airplane received substantial damage. The airplane was owned and operated by the pilot under the provisions of 14 CFR Part 91 as a personal flight that was not operating on a flight plan. Visual meteorological conditions prevailed for the flight that originated from Ralph, Michigan and was destined to BDJ. The Federal Aviation Administration coordinator for the accident investigation stated that he confirmed mechanical integrity of the airplane's flight controls, brakes, tail wheel, seat, and other systems during a post-accident examination of the airplane. He stated that on the day of the accident, the winds were south-southwest at 3 knots with gusts to 10 knots. The pilot made a tailwind landing. The pilot said that he may have made a mistake but did not know how. A witness said he observed the landing as a normal three point stall and as soon as the airplane began to roll out, it turned 20 degrees to the right and went into trees. The pilot did not provide a required National Transportation Safety Board Pilot/Operator Aircraft Accident Report and did not provide requested aircraft and pilot logbook(s) to the Federal Aviation Administration coordinator.