Today, most defensive coordinators will tell you that they are a spill team. That means they want to keep the ball going from side to side and prevent it from cutting up the field.
Each defense also uses the principle of a “holding player”. The container player is the player who stops the spill. In our 4-3 Defense, we say that everyone on the defensive front is a spill player, and one player (on each side) is the “box” player.
The box player simply boxes the play and forces her to return inside. That’s in a perfect world, of course.
Many coaches use the term “Force” the player instead of “Contain” or “Box” because they want the player to force the ball to change direction in some way. Either the ball carrier needs to turn to the inside, where the help is, or they need to bubble the ball to try and get around the forced player.
If the ball carrier is forced back, that gives the inside chase a chance to get there. It also means the player is closer to being pinned down on the sideline. The sideline is the 12th man in any football defense.
The 4-3 Defense is a true spill defense. Each player on the defensive front 7 is responsible for the inside half of their assigned space. He should almost collide with the blocker who is within his gap responsibility.
We call this “squeezing the air” out of space. Think about when you put something in a ziplock bag and squeeze out all the air before sealing it. By removing all the space between himself and the inside player in the space, the ball is forced, at worst, to continue outside of it.
As the players squeeze the air in the 4-3 Defense, we are building a wall of defenders for the ball carrier to maneuver. There should be no place for him to go up the field. Even the slightest crease can result in disaster. It only takes one player not being able to squeeze the air and we could be in trouble.
If each player does their job building the wall, the ball will continue out of the spill and eventually collide with the holding player or box player. The box player in our defense is usually the Strong Safety or Free Safety on the play side. We used quarter coverage to get both safeties involved in the run defense and create a 9-man front.
The final piece of the puzzle is the deep defenders. If we use quarter coverage, we have a 9-man front and two defenders who should always be above the #1 receivers. Step #1. These are the corners.
You can’t count on any defender who is responsible for a deep zone of the field, or who is locked into man-to-man coverage, for your running attacks. He is not in the spill, nor is he the box player. Our cornerbacks have the job of eliminating trick passes, play actions and other plays where wide receivers could pose a threat even after the offense shows up.