kangaroo court 
noun
An unofficial court held by a group of people in order to try someone regarded, especially without good evidence, as guilty of a crime or misdemeanour: they conducted a kangaroo court there and then...
- We have complained that it decides over important matters - the ownership of a domain name - but behaves more like a kangaroo court than a law court.
- They are treated as witnesses rather than prosecutors at the weekly kangaroo court known as the tribunal.
- Even the most properly constituted court is only a kangaroo court without a lawyer.