What is a first down in football?

The offense gets four attempts, called downs, to move the ball ten yards. Gain those ten yards and the count resets to first down with a new ten yards to go, which is why announcers say first and ten. Fail across all four downs and possession turns over to the opponent at that spot. That single mechanic drives almost all football strategy: it creates the yard-by-yard grind, defines what a successful play is, and explains why a three-yard run on first down is fine while the same run on third and eight is a failure.

Fourth down is where the math gets interesting. Because a failed fourth-down attempt hands the opponent excellent field position, teams traditionally punt to push them back, or attempt a field goal if close enough. Analytics have pushed hard against that convention over the past decade, showing that going for it on fourth and short is often the higher-expected-value choice, and NFL coaches now attempt it far more than they did a generation ago. Two related bits of vocabulary: the chains are the physical ten-yard measuring device brought onto the field for close calls, and a first down can also be awarded by penalty, which is why a defensive holding call can extend a drive that the offense failed to extend itself.