Technical differences between the 2-gap and 1-gap 3-4-
The 2-gap alignment puts both Ends in 4-techniques on the offensive Tackle’s head. The NG plays a 0 tech, on the Center’s head. Both offensive guards are uncovered by linemen, creating two bubbles over both guards in the defensive alignment. Inside LBs stand over the bubble in any defensive front to keep it gap-sound. See figure 2.
The gap that the DL attack is selected based on the release of the blocker. They wait to see which way he goes, and then squeeze the gap. If the OL goes outside, you squeeze his outer half – meaning you push him into the direction that makes the hole on his outside smaller. If he goes inside, you squeeze his inner half. You are tightening up the hole the RB intends to enter and keeping that OL off the LB who is supposed to make the tackle.
When you play a 2-gap 3-4 this way, you really need mammoth defensive linemen, and in particular the NG. They all have to control that blocker and be able to tackle on either side of him, which is difficult to do. The NG in any 3-4, 1 or 2-gap, is the most important player on the defensive front. Any 3-4 team without a good NG will have a bad run defense (see Georgia Tech).
Additionally, with 2 linebackers covering two bubbles, you require big inside backers who can handle a block from a guard on every play in the event that your linemen cannot keep them free.
The type of coverage and defense they then play, in part due to the size, is usually a read-and-react style. Defenses like this drop the linebackers in zone coverage most of the time and usually only one of the outside ‘backers is a "Rush" linebacker, who attacks off the edge to generate a 4-man pass rush. The most prominent example of this style nowadays is the New England Patriots. The contrary example of a blitzing two-gap 3-4 would be the Pittsburgh Steelers.
The one-gap version is set up as a more aggressive style of defense on every snap. I believe much of it can be accredited to Bum Phillips. His son Wade runs it still today. It is very closely analogous to Under front 4-3. Most pro teams that do not use the 3-4 are playing the Under. The two defenses are very similar
Like the Under defense, the one-gap 3-4 plays plenty of Cover 1 MAN coverage, with the idea being that the added QB pressure allows them to take a few risks in the pass defense. The Free Safety (FS) covers the deep middle of the field while the cornerbacks (CB) have man coverage outside and attempt to funnel their opponent towards the middle of the field where they have help.
Others continue the coverage schemes of the Pittsburgh Steelers with the zone blitz and matchup zone coverage. .
Matchup zone coverage is also called combination coverage. It is analogous to matchup zone in basketball: you are assigned a zone to defend, but any man who enters that zone is picked up man/man. The other type of zone is called spot-drop zone, where a defender drops to a spot on the field and remains there with his eyes on the QB so he can react to any throw.UGA plays a mix of combination coverage and man/man coverage schemes, but is primarily a C2 zone defense with rolling C3 against spread formations in their Nickel package. Since the one-gap 3-4 g defense like the Under 4-3, the man coverage isimarily based on man/man pressing packages using a single high safety and a "robber" underneath that is usually a linebacker. In any man/man scheme, the cover man is aligned with the correct leverage to funnel his receiver inside to the FS or to the boundary – i.e., towards the cover man’s best help. An alternative commonly used is 2 Man, with dual high safeties, that operates on the same concept.
Blitzes
Teams that use 3-4 schemes do use a few more zone blitz packages compared to Under 4-3 teams because in the case of the 3-4 you are usually blitzing and dropping linebackers, whereas in the 4-3 you’re dropping a DE. Zone blitz schemes catch the quarterback off-guard by dropping players into coverage where he assumes there will be a mismatch or uncovered zone because he reads a blitz. To be sound, and not give up big plays, they almost always have Cover 3 coverage behind them with a rotation of the coverage to one side (e.g., quarter-quarter-half instead of 1/3-1/3-1/3).
Now we want to illustrate a few blitzes from the 30-series fronts, both man/man and zone blitzes. There are obviously endless ways to blitz a QB and all have been thought of, but the choice of who to blitz and who to drop really depends on the individual talents of the player. It’s up to the coaching staff to identify those talents and utilize them the best way to win the ballgame.
The first simple blitz is a Combo blitz that alters based on the formation the offense shows. It can be a 2-gapped front or 1-gap. The secondary is in Cover 1 coverage and both OLBs blitz outside. When the offense presents a 2-back formation, the inside LBs take the first back that comes out to their side in man coverage. If one of them blocks, the free LB becomes a Robber.
At the end of the day Grantham's 3-4 is more a 1 gap/hybrid 3-4 vs. LeBeau's 2 gap sheme. The coverages played in college are more Vanilla behind the front seven and the NFL schemes ask more from the 3-4 backers in a wider array of schemes than in the college game.
The 2-gap alignment puts both Ends in 4-techniques on the offensive Tackle’s head. The NG plays a 0 tech, on the Center’s head. Both offensive guards are uncovered by linemen, creating two bubbles over both guards in the defensive alignment. Inside LBs stand over the bubble in any defensive front to keep it gap-sound. See figure 2.
The gap that the DL attack is selected based on the release of the blocker. They wait to see which way he goes, and then squeeze the gap. If the OL goes outside, you squeeze his outer half – meaning you push him into the direction that makes the hole on his outside smaller. If he goes inside, you squeeze his inner half. You are tightening up the hole the RB intends to enter and keeping that OL off the LB who is supposed to make the tackle.
When you play a 2-gap 3-4 this way, you really need mammoth defensive linemen, and in particular the NG. They all have to control that blocker and be able to tackle on either side of him, which is difficult to do. The NG in any 3-4, 1 or 2-gap, is the most important player on the defensive front. Any 3-4 team without a good NG will have a bad run defense (see Georgia Tech).
Additionally, with 2 linebackers covering two bubbles, you require big inside backers who can handle a block from a guard on every play in the event that your linemen cannot keep them free.
The type of coverage and defense they then play, in part due to the size, is usually a read-and-react style. Defenses like this drop the linebackers in zone coverage most of the time and usually only one of the outside ‘backers is a "Rush" linebacker, who attacks off the edge to generate a 4-man pass rush. The most prominent example of this style nowadays is the New England Patriots. The contrary example of a blitzing two-gap 3-4 would be the Pittsburgh Steelers.
The one-gap version is set up as a more aggressive style of defense on every snap. I believe much of it can be accredited to Bum Phillips. His son Wade runs it still today. It is very closely analogous to Under front 4-3. Most pro teams that do not use the 3-4 are playing the Under. The two defenses are very similar
Like the Under defense, the one-gap 3-4 plays plenty of Cover 1 MAN coverage, with the idea being that the added QB pressure allows them to take a few risks in the pass defense. The Free Safety (FS) covers the deep middle of the field while the cornerbacks (CB) have man coverage outside and attempt to funnel their opponent towards the middle of the field where they have help.
Others continue the coverage schemes of the Pittsburgh Steelers with the zone blitz and matchup zone coverage. .
Matchup zone coverage is also called combination coverage. It is analogous to matchup zone in basketball: you are assigned a zone to defend, but any man who enters that zone is picked up man/man. The other type of zone is called spot-drop zone, where a defender drops to a spot on the field and remains there with his eyes on the QB so he can react to any throw.UGA plays a mix of combination coverage and man/man coverage schemes, but is primarily a C2 zone defense with rolling C3 against spread formations in their Nickel package. Since the one-gap 3-4 g defense like the Under 4-3, the man coverage isimarily based on man/man pressing packages using a single high safety and a "robber" underneath that is usually a linebacker. In any man/man scheme, the cover man is aligned with the correct leverage to funnel his receiver inside to the FS or to the boundary – i.e., towards the cover man’s best help. An alternative commonly used is 2 Man, with dual high safeties, that operates on the same concept.
Blitzes
Teams that use 3-4 schemes do use a few more zone blitz packages compared to Under 4-3 teams because in the case of the 3-4 you are usually blitzing and dropping linebackers, whereas in the 4-3 you’re dropping a DE. Zone blitz schemes catch the quarterback off-guard by dropping players into coverage where he assumes there will be a mismatch or uncovered zone because he reads a blitz. To be sound, and not give up big plays, they almost always have Cover 3 coverage behind them with a rotation of the coverage to one side (e.g., quarter-quarter-half instead of 1/3-1/3-1/3).
Now we want to illustrate a few blitzes from the 30-series fronts, both man/man and zone blitzes. There are obviously endless ways to blitz a QB and all have been thought of, but the choice of who to blitz and who to drop really depends on the individual talents of the player. It’s up to the coaching staff to identify those talents and utilize them the best way to win the ballgame.
The first simple blitz is a Combo blitz that alters based on the formation the offense shows. It can be a 2-gapped front or 1-gap. The secondary is in Cover 1 coverage and both OLBs blitz outside. When the offense presents a 2-back formation, the inside LBs take the first back that comes out to their side in man coverage. If one of them blocks, the free LB becomes a Robber.
At the end of the day Grantham's 3-4 is more a 1 gap/hybrid 3-4 vs. LeBeau's 2 gap sheme. The coverages played in college are more Vanilla behind the front seven and the NFL schemes ask more from the 3-4 backers in a wider array of schemes than in the college game.

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