When I was a defensive coordinator, I installed our defense as more than a system. It was an attitude. Defense is about pursuit and passion. We installed our defensive attitude with a very specific process. I like to break things down into their simplest forms. Our defensive attitude revolves around getting the ball back as quickly as possible. There are three ways we can get the ball back:
1. We can force our opponent to punt
2. We can get a turnover or a turnover on downs
3. We can give up a score.
Ultimately, the 3 T's will determine which way we get the ball back.
First is our force concept. We have a player assigned to be the force player on every single play. We teach our force player that his landmark is the outside jersey number of the ball carrier. By attacking the outside jersey number of the ball carrier, our force player "forces" the ball carrier back into our players in pursuit. We tell our force player to take on the ball carrier as close to the line of scrimmage as possible. While we don't want to miss a tackle, our force player is coached to always take an angle where if he misses the tackle, he misses to his help. Our force player is typically going to be an invert/outside backer in our sky or cover 3 look, or a corner in Cloud or Cover 2.
The third concept of pursuit is called collapse. Our collapse players are typically our Mike backer and our defensive tackle or tackles, depending on our front. They are aiming one yard inside the ball carrier. They are responsible for the immediate cutback of the football. If they get a downhill run, they attack the middle of the man. They are spill players on trap plays.
Basic Concepts of the 30 Stack Defense