Wiktionary
fourth down
n. (context American football English) The fourth down in a series that has a maximum of four downs; often used to punt the ball downfield or attempt a field goal (If not punted or converted, the opposing team takes possession wherever the ball is).
Usage examples of "fourth down".
He had just discovered that if he stayed in the game through at least the fourth down card no matter what his hand (unless he knew he had no chance), his opportunity to win went up.
With just under five minutes left, Texas had a fourth down and three yards to go on its own forty-three-yard line.