On December 14, 1996, at 1645 hours Pacific standard time, a Robinson R-22 Beta, N8311A, rolled over upon colliding with the ground during an instructional flight at the Lampson Field, Lakeport, California. The helicopter was substantially damaged. The certified flight instructor (CFI) received minor injuries, and the student pilot was not injured. Visual meteorological conditions prevailed and no flight plan was filed. The flight originated from Lakeport at 1545. According to the CFI, seconds prior to the crash both he and his student were handling the flight controls. The CFI indicated that he had been instructing his student how to hover in ground effect when the student abruptly over controlled. The CFI further reported that he took the controls from his student a "little bit too late to correct" the student's over control. The main rotor blades struck the ground and the helicopter rolled over. In the CFI's completed report, he indicated that the level of the ground adjacent to his location sloped slightly upward, and he had misjudged the location of the horizon. The CFI further reported that no mechanical malfunctions were experienced with the helicopter or the engine. The CFI indicated that his student had about 4 hours of rotorcraft flying experience, and he had been a rotorcraft flight instructor for about 2 weeks.