In football, there are two philosophies on defense. You know about the difference between a 3-4 alignment and 4-3 alignment, but let's discuss the differences between a one-gap system and two-gap system.
There are six gaps along the offensive line (the four spaces between the five offensive linemen and the two at the end of the line) that need to be filled by the defense on each play. Coaches have developed two options to do this.
Let's examine both schools of thought.
We'll start with the Buffalo Bills' current one-gap, 4-3 system.
The one-gap system means six of the front seven defenders are responsible for one gap. Because you don't ever seen six down linemen outside of short-yardage situations, that means linebackers (or other second-level defenders) have to play a part in the foundation of this defense.
Each player only has to take care of one gap, therefore he's asked to attack upfield and disrupt the backfield. In essence... blow up his gap.
Beyond the Bills and Sean McDermott / Leslie Frazier, here are some notable coaches and teams that primarily utilize a one-gap philosophy:
- Jim Schwartz, Eagles
- Ron Marinelli, Cowboys
- Dan Quinn, Falcons
- Mike Zimmer, Vikings
- Ron Rivera, Panthers
- Teryl Austin, Lions
- Steve Spagnuolo, Giants
While this defense will occasionally feature twisting defensive linemen, blitzing linebackers, cornerbacks and safeties, you'll almost always notice the front defenders attacking. Rarely do defensive linemen drop into coverage in this system, because they need to account for their assigned gap.
The "ideal" front-seven defender in this defense is "smaller but faster" type. Here are some modern-day height and weight ranges for each player in a one-gap system in the NFL:
Defensive End: 6-foot-2 / 6-foot-5 and 255 / 275 pounds
Defensive Tackle: 6-foot / 6-foot-3 and 290 / 320 pounds
Linebacker: 6-foot / 6-foot-2 and 225 / 240 pounds
As you can probably piece together, the front four creating pressure is paramount in the one-gap system, and having linebackers with legitimate sideline-to-sideline speed is a huge luxury.
In the two-gap system, typically three down linemen are responsible for two gaps on either side of them. Because of that, they need to find where the football is first, then react it. Another byproduct of this tends to be defensive linemen who eat blockers at or near the line of scrimmage so the linebackers behind them – who account for the other gaps – can freely attack downhill and make plays.
Also, because of the three-man defensive line being outnumbered by two players up front, there's much more room and a need for creativity pertaining to defensive linemen dropping into coverage, overload blitzes from linebackers and cornerbacks, etc.
Creating offensive line and quarterback confusion is key to the two-gap defense.
Beyond former Bills head coach Rex Ryan, here are some notable coaches and teams that primarily utilize a two-gap philosophy:
- Bob Sutton, Chiefs
- Dom Capers, Packers
- Chuck Pagano, Colts
- Todd Bowles, Jets
- Dick Lebeau, Titans
- Vic Fangio, Bears
- Romeo Crennel, Texans
- Keith Butler, Steelers
- Dean Pees, Ravens
Also, front seven players – especially those along the defensive line – need to be larger in the two-gap system, so they're sturdier against double teams and are strong enough to use their arms to move defenders in their attempt to occupy gaps on either side of them.
Linebackers too need to be larger because they're going to have more offensive linemen climbing to them at the second level. The ability to take on and shed blockers are vital skills to possess as a defender in a two-gap system.
Here are some modern-day height and weight ranges for two-gapping defenders:
Defensive End: 6-foot-4 / 6-foot-7 and 275 / 310 pounds
Nose Tackle: 6-foot-1 / 6-foot-4 and 315 / 350 pounds
Outside Linebacker: 6-foot-2 / 6-foot-4 and 245 / 265 pounds
Inside Linebacker: 6-foot-1 / 6-foot-3 and 235 / 255 pounds
The two-gap system's effort is to win with power and confusion. While defensive linemen will rarely fill up the stat-sheet due to their double-gap responsibilities, a good two-gapping down linemen is extraordinarily valuable because of what he opens for his teammates. Linebackers, especially those on the outside, are highlighted in this defense.
Tying Each Gap System To Specific Numbered Alignments
The increased use of the nickel defense – one extra defensive back on the field instead of a linebacker – in the NFL because of the rapid rise in passing has blurred the line between 4-3 and 3-4 systems. However, there's still a clear distinction in gap assignments for those units.
The 4-3 defenses are almost universally one-gap systems, simply based on the numbers needed along the defensive line to account for four of the gaps. Wade Phillips' 3-4 is really the only defense known for predominant one-gapping.
Meanwhile, the 3-4 base defenses almost solely utilize the two-gapping philosophy.
Both one-gap and two-gap systems have been successful in the NFL today, but to have a better understanding of what you're watching on Sundays, it's important to know the size differences and contrasting responsibilities for the front seven in each defense.