The “snap” of the wrist, or rather the flexion of the wrist during the serving movement, is a highly debated and often misinterpreted subject in tennis. Biomechanical research shows that at the moment of impact there should not be many moving parts, the whole must be essential and “solid”, so there is nothing comparable to a rapid and forced movement of the wrist to influence the speed or trajectory of the impact. the service!
When we are in the phase of maximum external rotation of the right shoulder (i.e. when the racket is behind our right shoulder, totally vertical and with the head pointed towards the ground, also called the “racket drop” phase ) we are in the “point of no return” phase before the real acceleration of the racket towards impact.
Subsequently, an internal rotation of the shoulder takes place, which, along with forearm pronation (the movement that turns the palm of the hand from “facing the ear” to “facing the right side “), the racket to get the string – the bed turned over to the other side upon impact.
01. Maximum external rotation of the right shoulder (or racket drop phase); 02. Internal rotation of the shoulder, pronation of the forearm also begins; 03. Shortly before impact, pronation of the right forearm begins (to avoid “picking up” the ball with the edge of the frame), internal rotation of the shoulder continues; 04.
Closure of pronation of the right forearm, deceleration phase with end of internal rotation of the right shoulder. 
Since the acceleration phase is not controllable, since it takes place in a few milliseconds, it is what we do beforehand that guarantees a good success rate.
Of course, I can internalize the correct movement by doing “shadow swings”, or shadow movements, without the ball that are executed very slowly, to “feel” the correct movement. (…) One exercise that can help us “put the pieces together” of what we’ve seen so far is to simulate throwing the weight with a tennis ball. We start in the service position, left front foot parallel to the baseline, and we immediately move to the maximum load position, with the weight 75% above the rear (right) leg, the elbow high and away from the body at approximately 90°, right hip turned clockwise relative to the baseline, left arm extended and completely vertical, tennis ball in right hand, holding it loosely with the fingers, but simply placing it on the palm.
Here too, when launching, we make sure that the shoulders are on top of each other and not side by side at the same height. 01. “Shot put”. We start in the service position, left foot parallel to the baseline, and we immediately move to the maximum load position, with the weight 75% above the rear (right) leg, the elbow high and away from the body at approximately 90°, right hip turned clockwise relative to the baseline, left arm extended and fully vertical, tennis ball in right hand, holding it loosely with fingers, but simply resting on the palm.
02. During the jump, make sure the shoulders are on top of each other and not side by side at the same height.. The “shoulder on shoulder” position must be favored in any progression and this must lead us to correct the serving movement.
03. When we feel comfortable with the loading and throwing movement, we can insert the “jump” upwards and forwards, also emphasizing the arabesque, or the “kick” upwards of the right foot. This ensures that we have performed the jump with adequate explosiveness and allows us to work on the balanced exit of the serve movement.
During the throw we do not “jump” (we will stop at the step illustrated in image 02 above), we simply perform the movement by releasing the twist of the lower body and taking care of the moment that corresponds to the impact, stopping as the ball leaves the palm of your right hand.
The line joining the shoulders should be perpendicular to the ground and not parallel to it. (…) The goal is to throw the ball as high as possible, not as far. Once we feel comfortable with this movement we can also perform the exit jump
