Moving the goalposts (or shifting the goalposts) is a metaphor, derived from goal-based sports, that means to change the rule or criterion (goal) of a process or competition while it is still in progress, in such a way that the new goal offers one side an advantage or disadvantage.
In sports
Deliberately moving the goalposts constitutes a professional foul in rugby football and an unfair act in gridiron football. The officials are granted carte blanche to assess whatever penalty they see fit, including awarding the score for any attempt at a goal missed or invalidating any goal scored as a result of the moved goalposts. In both rugby and gridiron, goalposts are anchored into the ground; the distance they can be moved (most easily in gridiron by pulling down on one end of the crossbar to tilt both posts either to the left or the right) is far more restricted. Inadvertently moving the goalposts in a touchdown celebration is an unsportsmanlike conduct penalty of 15 yards against the offending team.
Moving goalposts is common in ice hockey, where physical contact with the posts is common. If the goalposts are...