goalpost

(sports) One of the two vertical side poles of a goal.

(sports, American football) The tall Y-shaped upright, now usually of fiberglass, at either end of the playing field, through which a football must go in order for a field goal to be scored. (They were originally H-shaped, with one wooden post on either side.)

A rule or target that is "moved" (changed) unfairly; see move the goalposts.