The certificated private rotorcraft pilot stated that the purpose of his flight was to practice flight maneuvers. He said that he was at a 3-foot hover when the right, rear skid made contact with the ground. The helicopter suddenly rolled onto its right side and sustained substantial damage to the tail rotor gearbox. The pilot did not report any mechanical or flight control anomalies. Winds about the time of the accident were from 250 degrees at 5 knots.