It seemed like the NFL Free Agency FAQ article I found yesterday was well received, (it was made a "sticky") so I thought I'd post the following article I found on defensive schemes. It was posted at KFFL on 8/18/04 but is still relevant now. I found it quite useful.
Defensive Schemes- 08/18/04
By Mark Mihalko - Edited By Cory J. Bonini
When it comes to defense in the NFL, there is no one defensive philosophy that is an absolute. Teams change schemes quite a bit trying to find the style that suits their players. Sometimes a change in scheme does wonders for a franchise. Look at the St. Louis Rams, after failing to stop anyone during the defense of their Super Bowl title, they brought in defensive coordinator, now Chicago Bears head coach, Lovie Smith who implemented the "Cover 2" schemes Indianapolis Colts head coach Tony Dungy made popular in Tampa Bay. The addition of Smith and an influx of speed in their front four returned them to Super Bowl contenders.
Changing schemes does not always work though. The Atlanta Falcons brought in former Buffalo Bills head coach Wade Phillips to change their defensive scheme to a base 3-4 style attacking defense, and the results were disastrous. Teams need to build their defense around their personnel and Atlanta's case they did not have the linebackers or secondary suited for that style of play.
Every defensive scheme in the NFL can be successful if they have the right players to make it succeed. Not every player fits a particular style of defense. A lot of defenses are a head coach's signature. For example, Pittsburgh Steelers head coach Bill Cowher has always used the base 3-4 scheme. While offensive-minded head coaches, such as the Rams' Mike Martz, allows his defensive coordinator complete control of the unit's identity. There is no right way for head coaches to handle this. Look at the last two Super Bowl champions the New England Patriots and the Tampa Bay Buccaneers. Defense was the staple of both units. However, The Patriots defense was built in the image of head coach Bill Belichick, who is always known for his defensive schemes. While in Tampa Bay, head coach Jon Gruden gave defensive coordinator Monte Kiffen complete control. Now let's look at the different styles of defenses in use throughout the NFL.
The "3-4" Defense
The 3-4 defense is making a comeback in the NFL. Teams like the Steelers, Baltimore Ravens and the Super Bowl champion Patriots are all using it successfully. Other teams like the New York Jets and San Francisco 49ers are attempting to install a similar style this offseason. The basic formation was devised by head coach Bud Wilkinson at the University of Oklahoma in the late 1940s. The alignment features three down lineman and four linebackers in the front seven, thus the name 3-4.
The three down lineman are generally giant run stuffing tackles, whose entire job is to keep the offensive line off of the linebackers. The most important down lineman is the nose guard, who lines up directly over the center and controls the middle of the field. Any pass rush received from the front three is a bonus.
The four linebackers are the heart and soul of this defense. They have to make plays both against the run and rushing the passer for this scheme to be successful. Usually teams will employ a rush linebacker, who is basically a stand-up defensive end, to continually apply pressure to the quarterback. The 3-4 alignment is an attacking style of defense and utilizes quite a few blitz packages to apply pressure. Teams are frequently using zone blitz schemes to add confusion to their blitz packages. This confusion can make a difference, even if the blitzer does not reach the quarterback.
If the linebacking corps is the heart-and-soul of a 3-4 alignment, the secondary is its backbone. Whether they use man-to-man or zone coverage this defense is only as good as the playmakers in the defensive secondary. The secondary faces a lot of pressure behind a 3-4 alignment. With the amount of blitzing utilized by the front seven, the defensive backfield is always on an island. The cornerbacks and safeties can use multiple coverages and alignments but are constantly in the spotlight if the linebacking corps fails to generate enough pressure on the quarterback. Teams that like to attack on defense usually use a "Cover 1" and "Cover 0" alignment. These are both man-to-man pass defenses that allow the team to place maximum pressure on a quarterback.
In "Cover 1" a fifth pass-rusher is added and there's a safety stationed in the middle of the field to help the cornerbacks cover deep routes. In "Cover 0", a sixth rusher is added and the safety is subtracted from the middle of the field.
Teams that utilize the 3-4 alignment believe in attacking the offense. The pressure and confusion generated by the blitz combinations can devastate even the most poised quarterback. However, with the specific player attributes required, it is one of the tougher alignments to find the proper personnel to run successfully.
Teams heading into the 2004 season who utilize this form of defense include: New England, Baltimore, Pittsburgh, Houston, Oakland and San Diego, with the Patriots and Raiders often switching their fronts between 3-4 and 4-3.
The "4-3" Defense
At this time, 26 NFL teams utilize a 4-3 defensive scheme. There are multiple coverage combinations that can be in play behind the front seven. Teams like the Indianapolis Colts and Tampa Bay Buccaneers use the 4-3 "Cover 2" system which is fast becoming the defense of choice in a lot of NFL cities.
Any 4-3 scheme, whether "Cover 2" or not is based on speed. Unlike the 3-4 system where the defensive linemen are tackles used to keep the linebackers free, the down linemen are the heart-and-soul of a 4-3 defense. There are similarities between the defenses though. Usually one of the two interior defensive tackles is a mammoth run stuffer that is used to clog the middle of the field. The other three defensive linemen provide the bulk of the pass rush for the defense. Teams that have a dominating front-four don't have to blitz to generate a pass rush and can utilize their three linebackers and four secondary members to defend the pass. Any 4-3 system uses smaller quicker defensive ends and tackles to aid in their pass rush. Developing a strong front four is critical in using any 4-3 scheme.
With the "Cover 2" scheme becoming so popular, people may ask, what exactly the "Cover 2" is. "Cover 2" is a pass-defense for teams with strong defensive linemen who don't require helping either rushing the passer or stuffing the run. It all starts with stopping the run with your down linemen because you don't have that eighth man in the box to help against the run.
By now, most everyone has heard of the term "Cover 2". Even though Tony Dungy made it a household name during his stint in Tampa Bay, the "Cover 2" was being played in the NFL long before Dungy was even a player in the league. It is one of the simplest alignments in football and it helps mask team liabilities in some areas. The basic principle is: Two half-field defenders and five guys underneath.
In "Cover 2", the two safeties are positioned deep and just outside the hash marks. Each safety is responsible for his deep half of the field. The underneath coverage consists of two corner backs responsible for jamming the wide receivers at the line of scrimmage. These cornerbacks fall into a zone coverage in the flat area. The three linebackers drop into a zone across the middle of the field, forming a line of defenders about 10 yards deep.
The basic idea of the defense is to eliminate the deep passing game by forcing teams to use their underneath or check down routes. The cornerbacks MUST get a good jam on the wide receivers to ensure proper defensive alignment.
This can be a great defensive system if the team has the personnel to utilize it. Finding the right defensive linemen for this scheme is one of the hardest things scouts and coaches have to do. The linemen must have a solid combination of size and quickness for this alignment to be successful.
Another popular coverage scheme is the "Cover 3" defense. In a "Cover 3" alignment one safety joins the two cornerbacks to form a three-deep alignment.
The other safety moves up and becomes the eighth man in the box. This gives the team one less underneath pass defender but does aid in stopping the run. Although this is one of the more conservative alignments on the defensive side of the ball, it is effective against both the run and the pass.
The "46" Defense
Teams like the Tennessee Titans and Philadelphia Eagles use a somewhat scaled down version of the famed "Bears 46 defense". Likely, anyone old enough remembers the dominating 46 defense used during the Bears' Super Bowl run in 1986. And for those who do not remember it, it is quite likely you have witnessed some variation of it in today's NFL.
Created by defensive coordinator Buddy Ryan the 46 defense evolved into a blitzing pass defense that sometimes left only three men in pass coverage. It was a high risk, high-reward defense designed to intimate and dominate offenses. In the 46, there were potentially eight pass rushers close to the line of scrimmage, and the blitzers would come from a variety of positions on the field.
The defensive line must be able to control offensive line, or use speed blow right past them. Between the defensive line and blitzers, quarterbacks must quickly check down to alternate receivers to be successful.
The most important element of a 46 defense is the secondary. Given the do-or-die nature of blitzing, the defensive backs are under constant pressure, they must be able to play bump-and-run and man-to-man coverage throughout the game, or the scheme will not succeed.
This super aggressive defense creates confusion and chaos. When there is a lot of confusion on the offensive side of the ball usually the defense wins.