The sixth part of the serve is getting from the trophy pose to something called the “racket drop.” It’s the first part of your swing. In this video we only focus on what the upper body is doing.
The video starts with me in the trophy pose. From the “L” position, I drop my tennis racket down behind my back so that it is pointed at the tennis court. Coaches sometimes refer to this position as “the scratch-back position” because it looks like I am trying to scratch my back with the tennis racket. Notice that my elbow comes up as I drop the racket down behind my back.
At 40 seconds in the video we now focus on my tossing arm. As i drop the tennis racket behind my back, I simply let my tossing arm fall straight down. Essentially, I let gravity do the work.
Finally, in the trophy pose my tossing shoulder is a little bit higher than my hitting-arm shoulder. However, when I get to the racket drop I want my shoulders to be about level. I always want my body sideways to the net. Another way to think about it is that I want my body to be facing the side fence.
At 1:15 in the video we look at some pictures of the pros transitioning from the trophy pose to the racket drop. We start with a picture of Serena Williams in her trophy pose. Her tossing arm is extended straight up in the air, her tennis racket and hitting arm are in an “L,” and her tossing shoulder is a little bit higher than her hitting-arm shoulder. In the next picture Serena is transitioning from the trophy pose to the racket drop. Serena is in the process of dropping the tennis racket down behind her back and, at the same time, she’s letting her tossing arm fall. That gets her to the racket drop in the subsequent picture. The tennis racket is pointed at the court behind her — kind of like she is scratching her back with the racket. Serena’s hitting-arm elbow has come up. Her tossing arm has continued to fall. Her shoulders have leveled out and her upper body is sideways to the net / facing the side fence.
At 2:12 in the video we see how John Isner transitions from the trophy pose to the racket drop. In the first picture Isner is in his trophy pose — tossing arm is extended straight up, tennis racket and hitting arm are in an “L,” and his tossing-arm shoulder is higher than his hitting-arm shoulder. In the next picture he is transitioning to the racket drop in the same way Serena was. The tennis racket is dropping behind his back and his tossing arm is coming down. That gets Isner to the racket drop, where the racket is pointed down at the court behind him, his elbow has come up, his tossing arm has continued to fall, his shoulders have leveled out, and his upper body is sideways to the net.