What it is

A ball is live when it is in play, and dead when the play is over. Whistles blow, and the ball becomes dead when a runner is down, steps out of bounds or a pass hits the ground.

In a game

Live-ball rules decide who can recover a loose ball. A fumble remains live, so either team can pick it up, while a dead ball cannot be advanced.

More detail

Some penalties happen before or after the ball is live, and have different results. For example, fouls on a dead ball are usually enforced from the next spot.