Why do you need at least two balls to play tennis?

Answer 1

because you get a second serve if you mess it up and if you mess up both serves the other opponent gets the point

Answer 2

Because you hit the ball with some kind of racket and that is why you call it a serve.

Answer 3

You don't NEED two balls to play tennis, it's just helpful to have another in your pocket to not spend an extra 30 minutes chasing tennis balls.

Answer 4

When the first serve is a let.