couper l'herbe sous le pied

to beat someone to an opportunity

Used when you nab the deal, the job or the idea before someone else gets the chance, leaving them with nothing to show for their own plans.

Il a signé le contrat avant moi, il m'a vraiment coupé l'herbe sous le pied.

He signed the contract before me, he really beat me to it.

Goes back to the 16th century, though the roots run further. In the 14th century 'herbe' could mean the leafy vegetables people lived on, and by extension came to stand for someone's means of subsistence, hence the older phrase 'l'herbe lui manque sous les pieds' for lacking the means to live. It seems to have then blended with 'couper les vivres' (cutting off someone's supplies), and the sense broadened from literal deprivation to being pipped at the post in any domain.