Today, most defensive coordinators will tell you that they are a spill team. This means they want to keep the ball on the sidelines and prevent it from cutting the pitch.
Each defense also uses the principle of a “player container”. The containing player is the player who stops the spill. In our 4-3 defense, we say that everyone in the defensive front is an overflow player, and one player (on each side) is the “box” player.
The box player, quite simply, boxes the game and forces it to come back inside. It’s in a perfect world, of course.
Many coaches use the term “Force” player instead of “Contain” or “Box” because they want that player to force the ball to change direction in some way. Either the ball carrier must turn inward, where the assist is, or he must return the ball to try to forcefully round the player.
If the ball carrier is forced to backtrack, it gives the inside chase a chance to get there. It also means the player is closer to getting pinned on the sideline. The sideline is the 12th man in any football defense.
The 4-3 defense is a real spill defense. Each player on the defensive front 7 is responsible for the inside half of their assigned gap. He should almost fall on the tackle who is inside his gap responsibility.
We call this “getting the air out” of space. Think about when you put something in a zippered bag and squeeze all the air out before sealing it. By taking all the space between him and the inside player in the gap, the ball is forced, at worst, to continue outside him.
As the players extract air into the 4-3 defense, we build a wall of defenders for the ball carrier to maneuver. There should be no room to step onto the pitch. The slightest fold can lead to disaster. It only takes one player to keep the air out, and we could be in trouble.
If each player does their job of building the wall, the ball will continue outside the spill and eventually collide with the containing player or the box player. The boxing player in our defense is normally the strong security or the loose security on the side of the game. We use quarterly coverage to involve both securities in the run defense and create a 9 man front.
The final piece of the puzzle is the deep defenders. If we use quarterly coverage, we have a 9-man front and two defenders who always have to stay above the No. 1 receivers. These are the corners.
Any defender who is responsible for a deep area of the pitch, or who is locked in man-to-man cover, cannot be counted on your attacks. He’s not in the spill, nor is the boxing player. Our corners are tasked with removing turn passes, game actions, and other games where wide receivers could pose a threat even after the run from offensive broadcasts.