The tennis serve is the most important single shot in the game of tennis. The serve permits the player to assert control over how the game unfolds, as the serve dictates how a particular return shot must be made. The successful service of the tennis ball is the product of a kinetic linkage that begins with the player's feet, extending through the legs, hips, shoulders, and wrist to the racquet on impact with the ball.
The first step in the proper mechanics of a tennis serve is the establishment of proper footwork. The player must begin the serve sequence from a stable position, where at the conclusion of the serve the player will be in a stance that permits an effective response to the next shot from the opponent. For a right handed player, the left foot will be placed immediately behind the boundary line, and the right foot behind. The player will ideally assume a balanced stance with the knees bent as the player prepares to execute the serve.
The most effective serve is one where the ball is struck by the player with elbow slightly bent, but the arm otherwise fully extended, making contact with the ball directly above the server's body. As the ball is tossed in the air to begin the serve sequence, the body is positioned to uncoil itself, with the full extension of this imaginary coil being achieved at contact with the ball. To achieve maximum power through this uncoiling mechanism, the twist of the player's torso, the swing of the racquet, and the drive upwards of the legs towards the ball all combine to generate greater speed in the racquet. As a general proposition of physics, the faster the racquet is moving upon impact with the ball, the faster the tennis ball will travel, as the greater racquet velocity translates into greater force directed into the ball and consequent velocity achieved by the ball on impact.
The racquet must be held securely but not tightly in the wrist and hand of the player. If the player grips the racquet too tightly, seeking to apply significant muscle power from the arm to the serve, the effective flow of energy generated by the movements of the rest of the body to the racquet will be defeated.
The precise point at which the ball is struck is also an important aspect of the mechanics of a tennis serve. If the ball is tossed too low, the player will not be able to fully extend the arm at impact. An incomplete extension of the arm and racquet decreases the amount of force directed into the ball on impact. A further consideration of a low service toss is that the lower the point of contact between ball and racquet, the greater chance that the ball will be delivered into the net. If the ball is tossed too high, studies have shown that the player will also hit the ball at a lower than optimal point; in visually tracking the ball thrown to a point above them, players tend to allow the ball to fall too far before striking it with the racquet. To preserve serve mechanics, the ball should be tossed to the desired height and struck on its ascent, at the moment the ball has reached the peak of its flight.
The concluding position of the player is also an important mechanical issue. As the player strikes the ball, the right foot of a right handed player will power through the stance, taking the player inside the court surface. The player must complete the serve in a bent knee (crouched) stance, in order to best react to the next shot of the opponent.