If someone hurt your reputation by way of slander or libel, you may have grounds to sue for defamation. In order to sue for defamation, you'll need to prove that the statement made against you was public, false, injurious and unprivileged.<quoted text>
It's my understanding that in order to file for defamation, there needs to be some kind of damage or loss, which is why monetary settlements are awarded if the plaintiff is successful. Nowhere in that filing does it mention what was the financial impact of the alleged false accusations that occurred.
So I think he has a good case. Of-course the "Tiny Casey Cheer Team" don't feel anyone other than Casey was hurt by her and her lies!