I would have like to see this in a more horizontal frame than a vertical, and it could probably use a little more strength in the colour. The three tennis balls is a little more distracting, as the concept makes me think that it is a variety of movements designed to hit one object, not several images all stuck on top of each other. You really only need one tennis ball, which will keep the focus on the player.
Very nice concept, the movement is very obvious in this. Something to keep in mind though, if you have something moving from side to side, it's best to give it room, meaning, you took this photo (these photos) vertically, but had you taken them horizontally, the subject would've had more room, this would make it more dynamic as a whole. Also, you'd miss the distraction that is currently there, because of the top of this photo.