Juggler's Tennis is a starting juggling move that all jugglers should learn once they master the regular 3 balls. Juggler's Tennis consists of juggling all three balls with one going over the top each time back and forth, like a tennis ball over a net.
1.) Start with two balls in one hand and one in the other 
2.) Toss the blue ball up.
3.) Now toss the green ball under it like you were normally juggling.
4.) This is where the trick comes in. The third ball, the red ball, is thrown over the other balls. This ball always travels over the top of the other balls.
5.) Now catch the blue ball and throw it normally, under the red ball.
6.) Catch the green ball and throw it normally, under the red ball.
7.) Catch the red ball and toss it back over the other two.
8.) Catch the blue ball and toss it back up.
9.) Catch the green ball and toss it back up.
10.) Catch the red ball and toss it back over the other two.
Repeat this over and over again and you are playing tennis with juggling balls.
Sorry there is no animator for this move yet. I'll have one soon, hopefully...Just follow the instructions and you should have no problem pulling off this trick.