After takeoff, the aircraft was observed to accelerate at a low height above the strip. At the upwind end, the pilot initiated a steep climb and a steep turn to the right, however the aircraft stalled at about 150 feet above the ground. The aircraft struck the ground heavily and slid into a ringlock fence. The pilot freed himself from the wreckage, and the engine which was still running at high speed, was shut down by a spectator. The pilot reported that after the ultralight stalled, he had the stick full back, but the aircraft would not recover. The aircraft stalled as a result of the steep climbing turn but recovery was not effected due to incorrect stall recovery technique.