Almost all of your joints are used in tennis, but the main ones in a tennis serve are the knee joints, and elbow joints.
You can hit an underhand serve in tennis; however, the overhand serve is more effective because it is more powerful. That is why you don't see the underhand serve used much.
Badly.
a serve
A tennis ball!
a tennis ball
A tennis ball.
A TENNIS BALL.
a serve
Fault
a fault
Yes