 There was a large contingent of Australian prospectors seeking their fortune in California at the time, and this, coupled with the reference to jumping, gave birth to the naming of the Kangaroo Court. The term then spread and was used for any sort of mock tribunal. The common expression, keep it up, means to continue do something, and is often used as a form of encouragement. And it dates from the 1700s and the game of badminton.