Leaving a clan, regardless of when they do it, does not violate any of Supercell's Terms of Service thus will never have a button to report them for any kind of infractions as NO infractions were made.
They also have a full spectrum policy of no name and shaming, so negative statistics will never be implemented without a wholesale change of Supercell's core policies and principles.
It happens to the best of us. People come and go. Some go at a very inconvenient time. Was there more we could have done as a clan to keep that player? I'm certain of it. Not everyone that leaves a clan early is a clan hopper, they more than likely just didn't like the clan. Not active enough, didn't relate to anyone, didn't receive the quality troops they expected, was poached by a bigger and stronger clan.... just because they leave doesn't make them a hopper.

