In American football terminology, a key is what a defensive player looks at prior to the snap of the ball. For example, if it’s first-and-5, odds are that the offense will attempt to run the ball. The defensive lineman must key (watch) the offensive lineman and be prepared to react to his movements.
Here’s a quick rundown of a defensive lineman’s thought process prior to any play:
Alignment: The defensive lineman has to make sure he’s aligned correctly.
Stance: The stance he’s using should be to his advantage.
Assignment: Does he know exactly what to do?
Key: The lineman considers what/whom he should be looking at.
Get off: He has to be quick off the football.
Attack: The lineman thinks about attacking and controlling the offensive lineman with his hands, and then escaping by using his arms and shoulder to push by him.
Execute: The lineman wants to execute his stunt to a specific area or gap, and then react to where the ball is.
Pursue: He always follows the football.
Tackle: Finally, he can make the tackle.
And you thought tackling was the only chore of a defensive lineman! Now you know that they have many responsibilities (some of them thankless tasks), and they really have to be thinking to put themselves in a position to make a tackle.