On May 7, 2011, at 2045 central daylight time, an unregistered Quicksilver model MXL II light sport airplane, was substantially damaged when it collided with terrain, near Crookston, Minnesota. The pilot sustained serious injuries. The airplane was operated by the commercial pilot, under the provisions of 14 Code of Federal Regulations Part 91. Day visual meteorological conditions prevailed for the flight, which was operated without a flight plan. The personal flight originated from the pilot's private airstrip near Crookston, Minnesota, at an unconfirmed time. The pilot stated that after completing a low pass over his private airstrip he decided to land. He reduced engine power to idle and entered a right turn back toward the airstrip. The pilot stated that while in the turn he did not reduce pitch to maintain adequate airspeed, which resulted in an aerodynamic stall/spin at low altitude. The airplane subsequently collided with terrain in a nose down and right wing low attitude. The fuselage and both wings were substantially damaged during the accident. The pilot stated that there were no preimpact mechanical malfunctions or failures that would have precluded normal operation of the airplane.