A Return Ace in tennis is when the receiver returns the serve so well that the server cannot hit the ball back. This wins the point immediately for the receiver.
Return aces are rare because the server usually has the advantage on their serve. It takes an incredible return to catch the server off guard and win the point outright.
Andre Agassi was known for his great return of serve and hit many return aces. His quick reflexes and ability to take the ball early helped him hit winners off the return.
Tennis Return Winners – [Return Ace][1]
[1]: https://www.youtube.com/watch?v=YsqMKYcGIfc