What are the mechanical differences between a volley serve and a drop serve?

USA Pickleball Rule 4.A governs the two permissible serving techniques. In the traditional volley serve (Rule 4.A.7), the ball is struck out of the air before bouncing; the server's arm must move in an upward arc at contact, the paddle head must be distinctly below the highest point of the wrist, and contact must occur below the navel. Conversely, the drop serve (Rule 4.A.8), introduced as an alternate delivery method, allows the server to release the ball from any natural height without tossing or propelling it downward. Once the ball bounces, none of the three upward arc/waist/wrist restrictions apply—the player may hit the ball at any height and paddle angle, provided their feet remain strictly behind the baseline.