The helicopter flight instructor reported that the student was practicing quick-stops on the taxiway. The student was hovering with a tailwind and began to accelerate when the helicopter started a "fast yaw to the right". He added that they stopped the acceleration, checked the engine gauges, and then accelerated again. As the helicopter was going through effective translational lift (ETL), it spun to the right. The flight instructor took the flight controls, noticed the rpm was high, and reduced the throttle. The helicopter impacted the ground backwards and slid before coming to rest. The helicopter sustained substantial damage to the vertical stabilizer. The flight instructor reported that there were no preaccident mechanical failures or malfunctions with the helicopter that would have precluded normal operation. A review of recorded data from the automated weather observation station located on the airport reported that, about 37 minutes before the accident, the wind was from 190° at 7 knots. The helicopter was taxiing to the north.