Last updated on 17-Apr-2008 04:38:21 PM
You certainly are allowed to serve with backspin that makes the ball bounce more than once.
When you serve the ball it has to hit your side and then your oponent's side. It is their responsibility to hit it after the first bounce on their side. Even if the ball spins back into the net it is still a good serve. Your opponent still has to try and hit it after the first bounce.
It is good to try and serve the ball short and with backspin. It can be a very effective serve for you.
It is impressive if you can already do this skill.