Hi Jeppe, great to hear youve been working on the reverse serve. I would say its a balance between the wrist strength and looseness you mentioned. You need to have the wrist relaxed enough so you can accelerate forward however when you contact the ball you need a little more wrist ‘strength’ so the contact is stable. If the wrist is too loose its difficult to feel the ball and control the length of the serve.
Try to experiment to find a balance, the best way is to try to get the feeling of being relaxed but then squeezing your fingers into the bat on contact with the ball.
