Generally speaking, the base defense of most football teams is either a 4-3 front (4 defensive linemen with 3 linebackers) or a 3-4 front (3 defensive linemen and 4 linebackers). With their base defense in mind, teams will fill their defensive rosters accordingly to fit the needs that their chosen base defense demands. The 43 and 34 fronts ensure one thing: the box will almost always have 7 defenders.
But in the last five or so years, the evolution of offensive philosophies and schemes, increasing levels of quarterback talent, and the use of analytics have really threatened the 43 and 34 defenses as base defensive schemes. The offenses of old used to do a lot of their play calling from:
21 personnel (2 backs, 1 tight end, 2 receivers); 7 potential blockers
22 personnel (2 backs, 2 tight ends, 1 receiver); 8 potential blockers
12 personnel (1 back, 2 tight ends and 2 receivers); 7 potential blockers
By using simple math, you can see why it was important to have at least 7 defenders in the box (not including safety) at all times to defend the run against these personnel groupings. In modern offensive football, however, we are seeing a continuing trend of more and more 11 personnel (1 back, 1 tight end, 3 receivers) usage.
Enter the ‘Nickel’ 4-2-5 (42) defense, which replaces one linebacker in the 43 with an extra defensive back. The typical specific personnel used in this formation is:
4 Defensive Linemen (2 DE/2 DT)
2 Linebackers (MLB/WLB)
5 Defensive Backs (3 CB/2 S)
This makes it much easier to matchup against 3 receivers against the pass by having a third corner on the field, but it still allows defenses to account for the run. For example, in a situation where your opponent scouting shows that offense has a tendency to run the ball, or when the offense adds blockers by using different personnel groupings or shifts/motions, the 42 defense can easily add an extra box defender with a safety (usually the SS) walking down into the box and have the same keys as an extra linebacker. This essentially turns the defense back into a 43.
In the above example, the offense is in the same formation as it was in the diagram against the 4-2-5 above, except this time, they have shifted the H receiver in tight. To account for this shift, the defense can shift as well. The SS walks down, the FS moves middle of the field, and the slot CB moves in tight as an overhang defender.
The beauty of the 42 is also a weakness of the 42. The 42 defense is a fast read formation. t does not allow the front 6 to play with much patience, they have to read hats and diagnose the play, fill their gaps quickly or get to their coverage assignment. This can present a problem against run-pass options (RPOs) and play action as shown below.
In the above example, the offense is using the aggressiveness of the 42 against them. The QB has the option to hand the ball off to the RB or throw the 1-step slant to the Z receiver. If the Will Backer comes up to fill his gap (he will), the QB will pull the ball from the RB and throw the slant behind him.
There are ways to minimize the damage that RPOs can do agains the 4-2-5.
SPACE BACKER – To prevent offenses from taking advantage of the linebacker aggressiveness that the 42 defense provides, many teams have created a new position entirely. I have always called it a “sub linebacker” but after researching the position, many teams at the college level are calling the position the “space backer”. This is a player who has the speed of a defensive back, but is usually a bit larger than the typical safety and can shed blocks and tackle well. They act as a “half linebacker, half safety” type player. This position will usually play to the wide side of the field in space, usually halfway between the inner-most slot receiver and the tackle. Since the Mike Backer is usually the best linebacker on a team, the Space Backer will generally replace the Will Backer.
SINGLE HIGH SAFETY – Another way a team can stop both the run and the run-pass options/play action is to drop the SS down low and move the FS to the middle of the field. You can still run all coverage shells with the SS walked down, and the front 6 can still be aggressive, filling and spilling against the run if needed.
Lets see the same RPO concept as earlier against the 4-2-5 with the SS low.
With the extra underneath defender, the front 6 are still moving forward to stop the run, but the SS who is now low is in the path of the frontside slant.
Sources and Research:
footballstudyhall.com – this website gave me the name “Space Backer” when researching the sub linebacker position, and they have a ton of great information.