Some kids were having a kickabout on the grass beside the walkway, cheering, groaning, calling for the ball, absorbed in the game, a self-contained universe marked out by jackets for goalposts and invisible touchlines.
A rule or target that is "moved" (changed) unfairly; see move the goalposts.
2012, Sarah L. Holloway, Mark Jayne, Gill Valentine, Alcohol, Drinking, Drunkenness: (Dis)Orderly Spaces, page 55:
[…] whatever you eat, how much you drink, you know the goalposts keep moving all the time, and it's difficult to be sure that, but I don't think it's harmful, not the amount I drink.