The 3-4 defense might be a team's best bet for a Super Bowl run in the modern NFL. Both of this season's title-game participants featured the scheme.
In fact, three out of the last five Super Bowls have been contested by teams that both ran 3-4 fronts. What makes it so popular in the modern NFL?
The simple answer is the 3-4's ability to counter the modern passing offense. Its flexibility, thanks to the presence of more versatile players, allows the 3-4 to disguise its intentions and cause confusion.
That makes it very unpopular with the most important player on offense.
Quarterbacks Hate It
Perhaps the best reason many teams love the 3-4 is because so many quarterbacks hate it. Drew Brees, the New Orleans Saints' record-setting gunslinger, recently bemoaned the difficulty of facing a 3-4 to Mike Triplett of The Times-Picayune:
You really have at least five rushers on the field at all times instead of four, with the ability to bring a lot of pressures where you've got all these hybrid guys on the field that, "Hey are they gonna rush the passer? You don't really want your running back blocking them. Are they dropping in coverage?" So they can be more multiple, I'd say, which can be more problematic for an offense.
Brees ought to know. He went 2-4 against 3-4 teams during the 2012 NFL season.
Consider the quarterbacks the San Francisco 49ers and Baltimore Ravens beat on their way to this season's Super Bowl. The 49ers used the 3-4 to first stifle Aaron Rodgers and then Matt Ryan. The Ravens baffled Andrew Luck, Peyton Manning and Tom Brady with the scheme.
What exactly is it that makes the 3-4 so tough on quarterbacks? It starts with a single, difficult question.
Who Is the Fourth Man?
That's the question a 3-4 poses to a quarterback on any given play. With four linebackers able to rush or drop and cover, the quarterback doesn't know how a 3-4 will set up a four-man rush.
The screen shot below, from Super Bowl XLVII, shows the problem in action.
The 49ers are in their base 3-4 alignment, showing the Ravens a zone look, with two deep safeties. Quarterback Joe Flacco is shown in the yellow circle, surveying this defense.
Flacco knows that any, or all four, of the 49ers' linebackers might blitz. The advantage the 49ers have is that their four linebackers will allow them to still create pressure and also match up with Flacco's receivers. The Ravens are showing two tight ends, two wideouts and one running back.
The 3-4 allows the Niners to counter this personnel and still rush Flacco into an errant throw, shown in the screen shot below.
At the snap, only one of the linebackers rushes the passer. Strong-side outside linebacker Ahmad Brooks blitzes and is matched up on running back Ray Rice in pass protection. The other three linebackers take away Flacco's two tight ends.
On the weak side, NaVorro Bowman (53) and Aldon Smith bracket Dennis Pitta. On the strong side, inside linebacker Patrick Willis (52) replaces Brooks in coverage and takes away Ed Dickson.
This is significant because it limits the number of receivers Flacco has to aim for. He is now committed to throwing into heavy coverage.
The screen shot below shows the Niners' 3-4 won the numbers game in coverage.
The blitz from Brooks takes Rice out of the play as a receiver. Willis, Bowman and Smith now have a three-on-two advantage over Dickson and Pitta.
That lets the 49ers cover two wideouts with four defensive backs. They have safety help, indicated by the black lines, on both of the Ravens' wide receivers.
This play is the essence of a 3-4. The 49ers have attacked a running back in pass protection, outnumbered receivers underneath and maintained a deep-coverage shell.
None of this could have happened for a 4-3 front. First, Rice would have released as a receiver, along with both tight ends.
The Ravens would then have had one-on-one matchups against three linebackers. This might have forced a safety down underneath to help. That would have created a single matchup on the outside for one of the wide receivers.
The 3-4 can also support larger coverage shells because of the number of people it can drop into coverage.
Another reason quarterbacks loathe the 3-4 is that it gives a defense greater potential to drop eight into coverage. Allow the masters of the 3-4 over the last two decades, the Pittsburgh Steelers, to demonstrate how in the screen shot below.
The play is from the Steelers' Week 11 matchup with the Ravens. The first thing to note, aside from asking yourself what on earth the Steelers are wearing, is how the Ravens have tried to spread the 3-4 out.
They have a tight end on the weak side over one outside linebacker, James Harrison. They have also positioned both wide receivers over on the strong side of the formation.
This forces the other outside linebacker, LaMarr Woodley, shown in the red circle, into a coverage alignment. It also brings the strong safety down from his deep rotation.
Because they are facing a potential mismatch on the strong side, the Steelers counter by dropping eight into coverage. Their linebackers play the key roles shown in the screen shot below.
On the weak side, Harrison has undercut the tight end's route shown in one red circle. In the other, Woodley and inside linebacker Lawrence Timmons double-cover wideout Anquan Boldin on the strong side.
The Steelers now have double coverage on all three primary receivers. As the play develops, the Steelers' linebackers help them bracket every one of Flacco's receivers. The screen shot below shows how it all unfolds.
It's clear that Flacco is being challenged to throw into heavy traffic. He eventually tried to force a deep pass to Torrey Smith. The throw was nearly intercepted by the over-the-top defender, shown in the blue circle, and fell incomplete.
Being spread out is something 3-4 fronts are facing more and more. Offenses are using tight ends, running backs and wideouts in slots and wide splits to try to expose linebackers in coverage.
However, some versions of the 3-4 are beginning to counter these spread tendencies.
1-Gap 3-4 Beating the Spread
The proliferation of 1-gap hybrid fronts has made it easier for 3-4 teams to deal with offenses that spread the field and pass on early downs. The Houston Texans are a prime example of this kind of 3-4.
The screen shot below shows Houston's 1-gap 3-4 countering a spread formation during its Week 10 matchup with the Chicago Bears.
Notice how the Bears have attempted to spread the Texans' linebackers out by aligning a tight end in the slot on both sides. They have also split running back Kahlil Bell (32) out wide on the strong side.
This shifts both outside linebackers out into coverage. The Texans realign their 3-4 front to combat this spread formation. The screen shot below shows how.
They start by moving both inside linebackers to the outside. They are shown in the red circles. Tim Dobbins (52) will cover tight end Kyle Adams (86) on the weak side.
Bradie James (53) will cover tight end Kellen Davis (87) on the strong side. On that same side, safety Danieal Manning drops down into coverage. His position is shown in the black circle.
The Texans have used their linebackers to create man coverage on both sides of the formation, with safety help over the top.
The position of Dobbins is significant because it means weak-side outside linebacker Connor Barwin is no longer needed in coverage. Barwin will instead blitz the pocket.
Notice the position of the Texans' three defensive linemen, each shown in a yellow circle. They are all shifted into a single gap.
The weak-side end is aligned between the left tackle and left guard in a 3-technique. The nose tackle is shifted into the strong-side A-gap between the center and right guard.
Strong-side end J.J. Watt is positioned outside the right tackle in a Wide 6 alignment. This is the 1-gap alignment of the Texans' 3-4. It differs from the 2-gap schemes of the 49ers and Steelers where every lineman is lined up directly over an offensive lineman.
The advantage is that 1-gap 3-4 linemen can create more pressure from these alignments. With only a single gap to attack, they can slant or stunt into those gaps and quickly get to the quarterback.
The screen shot below shows how the Texans' 1-gap front caused havoc for Jay Cutler and the Bears offense.
The 1-gap line and the blitzing outside linebacker immediately put Cutler under pressure. He attempts a deep pass to Davis.
The tight end is bracketed by James underneath and Manning over the top. Pressured by weak-side end Antonio Smith, who has quickly attacked his single gap, Cutler's errant pass was intercepted by Manning.
This play is a superb example of how the Texans' 1-gap 3-4 is really two defenses. By tweaking the positions of their three defensive linemen and moving linebackers around, the Texans show a 3-4 look, but attack with 4-3 principles.
Nobody combines elements of the 3-4 and 4-3 better than the new Super Bowl champions, the Baltimore Ravens.
The Super Bowl Champions and Mixing the 3-4 and 4-3
The Ravens have used a hybrid 3-4 since 2002. They have become experts at using the front to contain spread formations. The screen shot below, from Baltimore's AFC Wild Card Round victory over the Indianapolis Colts, shows a perfect example.
The Colts are attempting to spread the defense by aligning players in both slots, giving them four receivers. They also have an in-line tight end on the weak side.
The Ravens respond first by moving inside linebacker Dannell Ellerbe out to cover the weak-side slot. Then they move safety Bernard Pollard down to cover the strong-side slot. Their new alignments are shown in the red circles.
Pollard's position, in particular, is significant. By dropping down into man coverage underneath, Pollard allows outside linebacker/rush end Terrell Suggs to stay on the line.
Even though he is listed as an outside linebacker, Suggs plays more like a defensive end. The screen shot below demonstrates how the Ravens usually use Suggs and their outside linebackers.
From a three-point stance, Suggs will bring the pressure from the strong side, indicated by the red arrow. Suggs will usually position himself right on the line with his hand down. This gives the Ravens' 3-4 scheme its 4-3 appearance.
On the other side, outside linebacker Courtney Upshaw is also up at the line. However, Upshaw will drop out into coverage shown by the blue line. He will cover the tight end.
The screen shot below shows what this hybrid 3-4 concept can do to spread formations.
Suggs helps create a four-man rush, indicated by the red arrow. In the yellow circle, Upshaw has taken away the tight end.
Thanks to Pollard and Ellerbe's alignments, the rest of quarterback Andre Luck's receivers are locked up underneath. With Ray Lewis and Ed Reed covering the underneath and deep middle, the Ravens have the perfect coverage shell.
The play resulted in a desperate throw that fell incomplete. The Ravens presented a 4-3 look but retained core 3-4 principles.
By aligning both outside linebackers on the line, the quarterback can't be sure who is blitzing. It is usually Suggs, but a quarterback can never know that for certain.
Passing games have become far more expansive and sophisticated in recent seasons. Quarterbacks are now field generals, tasked with being coaches on the field.
More and more are being relied upon to call plays. The 3-4, with its inherent ability to morph into different guises, is the perfect weapon to confuse these quarterbacks.
Deception is the 3-4's best quality. The intentions of those four linebackers are never quite known until the last second.
It is a cloak-and-dagger defense that could be the best way to offset the dominance of the modern aerial offense.
All screen shots courtesy of NBC Sports, CBS Sports and NFL.com GamePass.