A fault.
A topspin serve in tennis is a serve where the player imparts forward spin on the ball, causing it to rotate forward as it travels over the net. This causes the ball to drop quickly and bounce higher when it lands, making it harder for the opponent to return. It is an effective serve for generating power and control.
Yes, this false start, along with serving with your racket above your waistline and moving your foot forward during the serve is illegal. You serve with one movement and one breath, basically. Any attempt to throw the receiver off is an unfair play, especially at the start of a game.
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.
a serve
Badly.
A tennis ball!
It depends on how hard you want to hit the ball
a tennis ball
Let
Yes
A tennis ball.