The amateur-built airplane was damaged during a forced landing following a loss of engine power while in the traffic pattern for landing. The pilot reported that the airplane's engine lost power "at the point of left downwind to base." He reported that the airplane was at 500 feet above ground level and over a river when the loss of power occurred. There was a soccer field with children playing on his left side and residences on his right side. He reported that he chose a field that he estimated to be 400 feet long and attempted an off-airport landing. He touched down on the left main landing gear first due to an incline in the field and trees and a brush pile that he avoided during the landing approach. He reported that the landing gear mount failed and the airplane slid to a stop. The pilot reported that subsequent to the accident the automotive style fuel line filter was found to be obstructed.