What it is

The secondary is the group of defensive backs: the cornerbacks and the safeties. They play behind the linemen and linebackers.

In a game

Their main job is pass coverage. They also help stop the run, especially safeties, who step forward when a runner gets past the line.

More detail

In passing situations teams add extra defensive backs, such as the nickel and dime backs, so the secondary grows from four players to five or six.