On July 30, 2002, at 0915 Pacific daylight time, a Robinson R22 Beta, N4074T, collided with the ground and rolled over while practicing quick stop maneuvers near Fresno, California. The helicopter sustained substantial damage. The commercial licensed flight instructor and a commercial pilot flight instructor candidate were not injured. The helicopter was operated by Mazzei Flying Service under the provisions of 14 CFR Part 91. Visual meteorological conditions prevailed and no flight plan had been filed. The local area instructional flight departed about 0900. In a written statement submitted by the CFI, he reported that after a series of maneuvers, he repositioned the helicopter and entered a quick stop over uneven terrain. He "misjudged the terrain and wind conditions" and the helicopter settled quickly to the ground. During the descent, the CFI raised the collective and the rotor rpm decreased. The helicopter impacted the ground, became airborne, and then impacted the ground a second time. During the impact sequence, the main rotor struck the tail boom. The helicopter came to rest on its left side. The accident site and helicopter wreckage were examined by a Federal Aviation Administration inspector. He reported observing a series of ground scars and wreckage debris that extended for 195 feet and culminated in the main helicopter wreckage. The first identifiable ground scars consisted of two parallel thin scars in the ground on the crest of a hillock, which were dimensionally consistent with the right and left skids; the scars extended 36 feet and terminated at the edge of a wash. At a distance of 105 feet across the wash, ground scars consistent with the tail rotor and stinger assemblies were noted; the tail rotor gearbox and blade assembly, along with the most aft portion of the tail boom, were found at this point. For the remaining 54 feet uphill to the location of the main wreckage, other ground scars and wreckage debris consistent with the skids were located.