I would like to leave a mark where my balls hit the pavement. Can anyone tell me the best way to do this and where to look?
What you are looking for is a decal.
Dastardly Bananas uses a Decal Manager in their FPS weapons script kit. You can hack this to make it work.
I've also written a small, easy-to-use decal script here:
http://forum.unity3d.com/viewtopic.php?t=60229
This might help you, as well.