An underhand serve is when a player holds the ball in one hand, swinging the other hand in the motion of a pendulum and releasing it at the tangential position, where the linear acceleration is maximum. The objective is to strike the ball from the bottom, which exerts a force in both the upward and forward directions, allowing the ball to gain velocity. A standard underhand serve is done in the following procedure:
Get into a ready position: Stand with your non-dominant foot in front of your dominant foot, with your toes facing forward, the dominant foot back pointing slightly outward. You may shift your centre of mass to the dominant foot. Your hips must face straight forward, with no angular displacement.
Hold the ball: Place the ball in your non-dominant hand, ensuring the ball is securely balanced and does not fall out of your hand. It might help to keep your fingers slightly loose to obtain a better grip on the ball. Fingers must not be used to grip the ball: the ball must be stable, not wobbly, but it has to be able to undergo motion when released.
Vertically displace the ball: With the ball placed at the height of your thigh, bring the ball closer to your body in front of the hitting arm. The purpose of this is to more easily exert a greater force by moving the body in the desired direction of the force.
Lean your shoulders forward: Move your hips back, whilst keeping your upper back straight. Bring the body closer to the ball to obtain greater control. Ensure that you are not standing up straight in this step; you may raise the toes on your front foot when positioning your hips.
Aiming: After deciding on a strategic place for the ball to hand, adjust your shoulder’s angle to the net; your back foot should move slightly to the right. Tracing a straight line, your eyes should be brought from the landing spot to where you will hit it. Squeeze your hitting hand into a fist.
Serving: Determine the resulting motion of the ball. Draw your hitting arm straight back, with the motion of a pendulum. Step forward as you swing your arm, shifting your weight to the non-dominant foot as you hit the ball.