A critical position for a big serve involves the tossing arm. After tossing the ball, you must extend your tossing arm until it points straight up to the sky (or even farther to the left like Djokovic). The student on the left does not fully extend his tossing arm and this prevents him from synchronizing his arms with his upper body coil.

Djokovic is in the perfect fully coiled position "trophy" position. His racket points straight up to the sky, his tossing arm points straight up to the sky, and his upper body is fully coiled, chest almost facing the sky. His upper body and arms will work together.