What happens if clan leaders abuse their power?

Solution 1:

Clans in Clash of Clans are considered to be property of the leader. With that said, a leader can invite or expell anyone who he pleases, and that does not break the rules.

The only exception is when inviting and expelling breaks war rules (by exploiting a loophole of sorts).

Other than that there is no reason to report a clan leader, unless he is cheating (or exploiting the system) or alternatively being verbally abusive.

If any other member abuses it's up to the leader to decide what to do with him.

Solution 2:

They wouldn't punish them at all. Especially if it was the leader, as it is their clan, so they can run it how they wish, and people are free to join which ever clan will let them, and can leave anytime they wish. If a leader is kicking people to be funny though, I would imagine that people would leave his clan pretty quickly, and soon he wouldn't have any members to kick.

Solution 3:

You cannot do anything.

Vote with your feet - find another clan.