According to the pilot's statement, he made a radio call he was entering left base of the traffic pattern for the runway. He heard another radio call for an airplane taxiing to the runway and saw the airplane approaching the run-up area. The pilot made a radio call he was turning onto final for the runway. He saw the other airplane move toward the runway hold short line and he made another announcement he was on final approach for the runway. As he approached the runway end, the other airplane "nosed over the line." During the landing flare at midfield, the other aircraft made a radio call to takeoff on the runway. The pilot attempted to depart the runway area for the taxiway. As he turned the helicopter toward the taxiway, he felt the helicopter "swing hard and turn," then begin to spin. The pilot stated he lost control and landed hard "crushing" the skids.