when the chips are down

when the chips are down  {adv. cl.},  {informal}

When the winner and loser of a bet or a game are decided; at the most important or dangerous time.

Tom hit a home run in the last inning of the game when the chips were down.

When the chips were down, the two countries decided not to have war.

(From the fact that in gambling games, a person puts chips or money down in front of him to show that he is willing to risk an amount in a bet.)