During an introductory training flight, the instructor attempted to demonstrate a hovering maneuver around a point on the ground. The wind at the time of the accident was estimated by the instructor to be 15 to 20 knots out of the south. During the maneuver when the helicopter was near downwind, the instructor lost control of the helicopter and it started to rotate in an uncontrollable right yaw. The instructor reported that the helicopter continued to spin until hitting the ground and rolling over approximately 300 feet from the initiation of the loss of control. The helicopter sustained substantial damage to the tailboom and main rotor drive system. The reported wind at the time of departure was from 180 degrees at 18 knots, gusting to 25 knots. The instructor reported no mechanical malfunctions prior to the accident.