Avoid breaking your wrist and instead keep the racket angle stable through impact, focusing on acceleration and a compact swing to generate pace and backspin.
This covers a very common mistake people make with their volleys. The coach is right, trying to add too much flick with your wrist actually takes power and control away. Focusing on keeping the racket angle and using acceleration is the key to getting that sharp bounce off the glass. It's a simple principle but often difficult to implement if you're used to overcomplicating the shot.
