1834, from goal (n.) + post (n.1). To move the goal posts as a figurative expression for "cheat by changing the objectives after the process has begun" is by 1988.
Entries linking to goal-post
goal n.
1530s, "end point of a race," of uncertain origin. It appears once before this (as gol), in a poem from early 14c. and with an apparent sense of "boundary, limit." Perhaps from Old English *gal "obstacle, barrier," a word implied by gælan "to hinder" and also found in compounds (singal, widgal). That would make it a variant or figurative use of Middle English gale "a way, course." Also compare Old Norse geil "a narrow glen, a passage." Or from Old French gaule "long pole, stake," which is from Germanic. Sports sense of "place where the ball, etc. is put to score" is attested from 1540s. Figurative sense of "object of an effort" is from 1540s.
post n.1
"a timber of considerable size set upright," from Old English post "pillar, doorpost," and from Old French post "post, upright beam," both from Latin postis "door, post, doorpost," in Medieval Latin "a beam, rod, pole," which is perhaps from Vulgar Latin *por- "forth," a variant of pro- (see pro-) + stare "to stand" (from PIE root *sta- "to stand, make or be firm").
Similar compounds are Sanskrit prstham "back, roof, peak," Avestan parshti "back," Greek pastas "porch in front of a house, colonnade," Middle High German virst "ridgepole," Lithuanian pirštas, Old Church Slavonic pristu "finger" (PIE *por-st-i-).
Later also of metal. As a type of hardness, lifelessness, deafness by early 15c.