I remember an incident in the Middle East when I was behind a puma that was engaged n the ground idle process of shutting down, suffering a tail rotor pitch failure resulting in a full hardover to,I think, port, akin to full left pedal. Even though at ground idle and on the ground, the aircraft yawed violently. I can't remember the cause, maybe an actuator failure, but if that had happened in flight I cannot think of any remedy which would have resulted in a succesful outcome.