|“||In general, ideal front-seven players in the 3–4 are bigger and need to take on and defeat blocks more often in the running game.||”|
The 3–4 defense declined in popularity over the years, but has found renewed use by modern professional and college football teams. The 3–4 defense is so named because it involves 3 down linemen and 4 linebackers. There are usually 4 defensive backs.
Teams that regularly incorporate the 3-4 defensive alignment scheme include the Cleveland Browns, San Diego Chargers, Green Bay Packers, Baltimore Ravens, Arizona Cardinals, Indianapolis Colts, Kansas City Chiefs, New York Jets, San Francisco 49ers, Pittsburgh Steelers, Washington Redskins, New Orleans Saints, Philadelphia Eagles and Houston Texans. The Cardinals already incorporate the 5–2 defense, an older variation of the 3–4, in some of their defensive schemes. The Miami Dolphins have also incorporated elements of the 3–4 defense into their scheme, under defensive coordinator Mike Nolan, but with the hiring of Kevin Coyle as their new defensive coordinator, the Dolphins will switch to a 4-3 Defense under new coach Joe Philbin. The Ravens run a hybrid defense and occasionally shift to 4–3 schemes during games. With the hiring of defensive coordinator Dom Capers, the Green Bay Packers have switched to a 3–4 defense (2009). With the hiring of Chuck Pagano as their new Head Coach, the Indianapolis Colts have switched to 3-4 Defense. The Buffalo Bills installed a 3–4 scheme to begin the 2010 season, but made frequent use of 4–3 sets as the season progressed, and will stick with the 4-3 for 2012 following the signing of free agent defensive end Mario Williams. Under defensive coordinator Wade Phillips, the Houston Texans have adopted the 3–4 defensive scheme for the 2011 season. The Dallas Cowboys will switch to the 4-3 Defense with the hiring of Monte Kiffin as their Defensive Coordinator. Sean Payton announced that the Saints will switch to the 3-4 Defense for the 2013 season, and the Cleveland Browns will switch to a 3-4 "stick-em" defense. With the hiring of Chip Kelly as Head Coach and Billy Davis as Defensive Coordinator, the Eagles will shift to a hybrid defense that will incorporate 3-4 and 4-3 schemes.
Typically, there are two major variations of the 3–4 defense. Both variations are directly related to coverage schemes on obvious passing downs. For the first type, the outside linebackers will rush the quarterback, the great majority of the time. This defensive scheme is largely attributed to Dick LeBeau, although there is some discussion that Joe Collier of the Denver Broncos "Orange Crush" was the actual originator of the "NFL 3–4" . In the 1970s the Miami Dolphins would bring in Linebacker Bob Matheson (number 53) to be a fourth linebacker in passing situations, a formation known as the "53 Defense." On key situations, the rush linebacker will be sent to cover the flat on the opposite side of the blitzing defensive back; this is the infamous "zone blitz". The other common 3–4 defense is typically associated with the New England Patriots. This scheme requires outside linebackers to have the ability to back pedal and drop into coverage. Of course they do rush the passer at times, it is just that they are much more likely to drop into coverage.|
The Chicago Bears are the only NFL team that have never used the 3–4 as their base defense. Before the 2010 season, the Washington Redskins had also never run a base 3–4, but under the direction of new defensive coordinator Jim Haslett, the Redskins have adopted the 3–4 and its many variants, such as the 2–4–5 and the 1–5–5, based on formations used by the Pittsburgh Steelers.
Conversely, the Steelers have used the 3–4 as their base since 1982, the season after Pro Football Hall of Fame defensive tackle Joe Greene and end L. C. Greenwood retired. In fact, the Steelers were the only NFL team to use the 3–4 defense during the 2001 NFL season, but finished the season as the number one defense in the NFL. It is believed that the Steelers success with the 3–4 defense is the primary reason why many NFL teams have started returning to the formation.
The 3–4 defense was originally devised by Bud Wilkinson at the University of Oklahoma in the 1940s. Chuck Fairbanks learned the defense from Wilkinson and is credited with importing it to the NFL. The 1972 Miami Dolphins were the first team to win a Super Bowl with the 3–4 defense, going undefeated and using number 53, Bob Mathison as a down lineman or rushing linebacker. When the Oakland Raiders defeated the Philadelphia Eagles in Super Bowl XV, it marked the first Super Bowl in which both teams used the 3–4 as their base defense. Also notable, the Big Blue Wrecking Crew, the defensive unit for the 1986 New York Giants who won Super Bowl XXI, was a 3–4 defense and featured all-time great Lawrence Taylor as outside linebacker. By the mid-1990s, only a few teams used a 3–4 defense, most notably the Buffalo Bills and Pittsburgh Steelers.
Defensive line 
|“||The nose tackle and the inside linebackers, those are three guys that are very important. But when you go through it, the nose tackle is probably the single-most important guy.||”|
The defensive line is made up of a nose tackle (NT) and two defensive ends (DEs). Linemen in 3–4 schemes tend to be larger than their 4–3 counterparts to take up more space and guard more territory along the defensive front. 3–4 defensive ends were usually defensive tackles (DTs) when entering at first. They must be strong at the point of attack and are aligned in most cases head-up on an offensive tackle. First and foremost, they must control run gaps. Size and strength become more of a factor for linemen in 3–4 defenses than in 4–3 defenses because they move primarily within the confines of line play and seldom are in space using athletic ability. Ideally 3–4 DEs should weigh 285–300 pounds (129–140 kg) and be able to beat double teams by getting a push. The 3–4 nose tackle is considered the most physically demanding position in football. His primary responsibility is to control the “A” gaps, the two openings between the center and guards, and not get pushed back into his linebackers. If a running play comes through one of those gaps, he must make the tackle or control what is called the “jump-through”—the guard or center who is trying to get out to the linebackers. The ideal nose tackle has to be much bigger than 4–3 DTs, weighing around 330 pounds or more. Ted Washington is considered the prototypical nose tackle of this era. “In his prime, Ted Washington was the ideal guy,” says an AFC pro personnel director. “He was huge, had long arms, and you couldn't budge him. He could hold off a 320-pound lineman with one hand and make the tackle with the other.” Since most college teams run a 4–3 defense, most college DTs are more of a 4–3 tackle than a true nose tackle, which makes good 3–4 NTs hard to find.
The base position of NT is across from the opposing team's center. This location is usually referred to as zero technique. The two DEs flank the NT and line up off the offensive guards. The location off the offensive guard is usually referred to as three technique.
Some 3–4 teams (such as the Pittsburgh Steelers) use the three down linemen primarily to occupy the offensive linemen. In such systems the defensive linemen are assigned two gaps to defend. The NT is responsible for defending plays which occur in the spaces, or gaps, between the center and guards. Each of those spaces is called an A gap. Flanking the NT, DEs defend the gaps on either side of the tackle he lines up across from. Each guard-tackle gap is a B gap and the space outside each tackle is called a C gap. Other 3–4 teams (such as the San Diego Chargers and the Dallas Cowboys) primarily make each lineman responsible for only one gap.
According to former general manager Randy Mueller, “the 3–4 defensive end is easier to identify and find when it comes to scouting and acquiring personnel,” while 4–3 DEs “are rare and hard to find and therefore very expensive to keep. There is no question that speed pass rushers are very much an impact position on the football field and their cap numbers reflect that. On the other hand, 3–4 defensive ends can be found easier and are much less expensive when it comes to ‘cap dollars’.”
|“||I think good coaches will coach with the personnel they have, and if you only have one (good) linebacker, you’re not going to play a 3–4.||”|
In a 3–4 defense, four linebackers (LBs) are positioned behind the defensive line. The linebacker unit is made up of two inside linebackers (ILBs) flanked by two outside linebackers (OLBs). The OLBs often line up closer to the line of scrimmage than the ILBs, but may also be positioned at the same depth or deeper in coverage than the ILBs (though this is somewhat rare).
Strengths of the 3–4 include speedy ILBs and OLBs in pursuit of backs in run defense and flexibility to use multiple rushers to confuse the quarterback during passing plays without being forced into man-to-man defense on receivers. Most teams try to disrupt the offense's passing attack by rushing four defenders. In a standard 4–3 alignment, these four rushers are usually the four down linemen. But in a 3–4, the fourth rusher is usually a linebacker, though many teams, such as the Pittsburgh Steelers and Baltimore Ravens, use a talented safety to blitz and confuse the coverage, giving them more defensive options in the same 3–4 look. However, since there are four linebackers and four defensive backs, the fourth potential rusher can come from any of eight defensive positions. This is designed to confuse the quarterback's pre-snap defensive read.
A drawback of the 3–4 is that without a fourth lineman to take on the offensive blockers and close the running lanes, both the defensive linemen and the linebackers can be overwhelmed by blocking schemes in the running game. To be effective, 3–4 linebackers need their defensive line to routinely tie up a minimum of four (preferably all five) offensive linemen, freeing them to make tackles. The 3–4 linebackers must be very athletic and strong enough to shed blocks by fullbacks, tight ends, and offensive linemen to get to the running back. In most cases, 3–4 OLBs lead their teams in quarterback sacks.
Usually, teams that run a 3–4 defense look for college “tweeners”—defensive ends that are too small to play the position in the pros and not quite fluid enough to play outside linebacker in a 4–3 defense—as their 3–4 outside linebacker. The wisdom of this strategy is demonstrated in the career of Harry Carson, who played as a defensive lineman in his college career and then went on to become a Hall of Fame ILB for the New York Giants in the 70's and 80's. According to NFL coach Wade Phillips, 3–4 linebackers “are a little bit cheaper, and you can find more of them,” while “it's harder to find defensive linemen to play a 4–3 and pay for all of them.”
The 3–4 defense generally uses four defensive backs. Two of these are safeties, and two of them are cornerbacks. A cornerback's responsibilities vary depending on the type of coverage called. Coverage is simply how the defense will be protecting against the pass. The corners will generally line up 3 to 5 yards off the line of scrimmage, generally trying to "Jam" or interrupt the receivers route within the first 5 yards. A corner will be given one of two ways to defend the pass (with variations that result in more or less the same responsibilities): zone and man-to-man. In zone coverage, the cornerback is responsible for an area on the field. In this case, the corner must always stay downfield of whomever it is covering while still remaining in its zone. Zone is a more relaxed defensive scheme meant to provide more awareness across the defensive secondary while sacrificing tight coverage. As such, the corner in this case would be responsible for making sure nobody gets outside of him, always, or downfield of him, in cases where there is no deep safety help. In man coverage, however, the cornerback is solely responsible for the man across from him, usually the offensive player split farthest out.
The free safety is responsible for reading the offensive plays and covering deep passes. Depending on the defensive call, he may also provide run support. He is positioned 10 to 15 yards behind the line of scrimmage, toward the center of the field. He provides the last line of defense against running backs and receivers who get past the linebackers and cornerbacks. He must be a quick and smart player, capable of making tackles efficiently as well as reading the play and alerting his team of game situations.
The strong safety is usually larger than the free safety and is positioned relatively close to the line of scrimmage. He is often an integral part of the run defense, but is also responsible for defending against a pass; especially against passes to the tight-ends.
NFL teams using a 3–4 base defense as of 2013 
- Arizona Cardinals
- Baltimore Ravens
- Cleveland Browns
- Green Bay Packers
- Houston Texans
- Indianapolis Colts
- Kansas City Chiefs
- New Orleans Saints
- New York Jets
- Pittsburgh Steelers
- Philadelphia Eagles
- San Diego Chargers
- San Francisco 49ers
- Washington Redskins
While Patriots coach Bill Belichick hasn't formally announced a shift to the 4–3, media speculation has been rampant after the team acquired 4–3 specialists like Albert Haynesworth, Mark Anderson, Shaun Ellis, and Andre Carter. The Patriots debuted their 4–3 defense in week one of the 2011 season. Five of New England's six sacks in its week one victory over the Miami Dolphins came from defensive linemen. However, during Super Bowl XLVI, the Patriots began the game using a 3-4 Defense. As of 2012, the team has returned to a 4-3 base.
While many still consider the Baltimore Ravens' defense a 3–4, it has shifted towards a 4–3 scheme since 2006 when half their games were in a 4-3 base defense. The Ravens' primary pass-rusher, Terrell Suggs, played the majority of his snaps in 2010 as a true defensive end.
The 49ers run a hybrid 3–4 defense that attack offenses using both 3-4 and 4-3 principles. The 49ers' hybrid rush linebacker, Aldon Smith, occasionally lines up at defensive end.
With the hiring of Kevin Coyle as their Defensive Coordinator, the Miami Dolphins will make a switch to a 4-3 Defense. Coyle was a defensive assistant under Head Coach Marvin Lewis in Cincinnati, which ran a 4-3 Defense, but new Head Coach Joe Philbin's Packers ran a 3-4 Defense with Dom Capers as Defensive Coordinator and Philbin was the Offensive Coordinator.
On January 31, Bills coach Chan Gailey announced to Sports Illustrated that the Bills will switch to a base 4-3 Defense for the 2012 season, though they will continue to use variances of a 3-4 Defense.
With the hiring of Chuck Pagano as Head Coach, the Indianapolis Colts will go to a 3-4 Defense, which will likely involve moving pass rushers Dwight Freeney and Robert Mathis from Defensive End to Outside Linebacker. It is now rumored that Freeney will probably get traded to a team that runs a 4-3 Defense.
The New York Jets will use a base 4-3 Defense for the 2012 Season with the addition of Quinton Coples as a Pass Rusher, but will switch to a 3-4 Defense on occasion. The Jets decided to stick to the 3-4 Defense as its base defense for the 2012 Season.
The Kansas City Chiefs are expected to return to a 4-3 Defense with Andy Reid being named their Head Coach. Reid prefers a 4-3 scheme, which he operated in Philadelphia with Jim Johnson and subsequent Defensive Coordinators. However, with the hiring of Bob Sutton from the New York Jets as Defensive Coordinator, the Chiefs have decided to remain a 3-4 Defense under Andy Reid.
When the Cleveland Browns hired Rob Chudzinski as a head coach, it was believed he wanted an attacking 3–4 defense. The hire of former Arizona Cardinals defensive coordinator for the same position in Cleveland backs up that belief.
It is believed that newly hired Philadelphia Eagles coach, Chip Kelly, would change the Eagles defense to 3-4. Defensive coordinator Billy Davis announced that he will implement the "Predator", a hybrid defense that incorporates both 4-3 and 3-4 principles.
On January 22, New Orleans Saints Head Coach Sean Payton fired Defensive Coordinator Steve Spagnuolo and announced that team will shift to a 3-4 Defense. The hiring of Rob Ryan as defensive coordinator confirms the switch.
FBS College Teams that use 3-4 as base defense 
- Alabama Crimson Tide
- Oregon Ducks
- Georgia Bulldogs
- Kentucky Wildcats
- Notre Dame Fighting Irish
- Stanford Cardinal
- Georgia Tech Yellow Jackets
- UCLA Bruins
- Air Force Academy
- Wisconsin Badgers
- Breer, Albert (2009-02-22). "Finding players who fit 3–4 scheme more art than science". The Sporting News.
- Tanier, Mike (2006-08-28). "The 4–3 vs. the 3–4". NFL on Fox.
- Legwold, Jeff (2009-01-23). "Former Broncos defensive coordinator Collier explains art of 3–4 defense". Rocky Mountain News.
- Smith, Michael (2004-12-15). "Defensive linemen do the dirty work in 3–4". ESPN.com.
- Dillon, Dennis (2004-10-11). "Getting their nose dirty". The Sporting News.
- More defenses find 3–4 scheme tempting
- NFL.com: Effectiveness of 3–4 vs. 4–3 is found in the numbers
- Bouchette, Ed (2007-04-27). "Not all linebackers and defensive ends are created equal". Pittsburgh Post-Gazette.
- McLane, Jeff. "Eagles have hired Chip Kelly to be their next head coach". philly.com. Retrieved 2013-01-19.