In the Chalk Talk Random Question Thread, I've noticed that alot of people want to talk defense. So, here's some defensive talk
With all things in football, different teams use different philosophies. I'll share with you the ones I use. To determine offensive strength, the first thing you look for is a tight end. If a single tight end is present, the side that the tight end aligns to is your strength call. If there is no tight end, or a balanced look, you look for the next possible strength check:
Multiple Receivers. The side with more receivers, once tight end side has been determined as an unusable check, now becomes your strength. If that check doesn't work, you check
Where the running back is aligned. If there's one back, and he's aligned to the right of the quarterback, it's a strong right call.
And the last one we use is the arm of the quarterback. In a formation where it's perfectly symmetrical (like an ace formation, or a bone formation) the hand that the quarterback throws with helps us to determine our strength.
Now, keep this in mind, our strength calls are extremely dumbed down. In college we used two separate strength calls. One to determine run strength and one to determine pass strength. But this is kind of a easy way to check strength calls.
There are two types of fronts in football, the odd and the even front. Quite simply put, an odd front has an odd number of players on the line of scrimmage and an even front has an even number of players on the line of scrimmage.
A 3-4 defense technically means that there are three down linemen and four linebackers, hardly a ground breaking thought... But when those two linebackers are also on the line of scrimmage it becomes a five front. Now, that doesn't change the frontage... A 3 man front and a 5 man front are both still odd fronts.
The primary difference between the two types of fronts are the use of a nose tackle. Perhaps the word "nose tackle" is a poor choice here, as some 4-3 defenses utilize a nose tackle as well, but they align themselves differently.
In an odd front, you'll primarily see a nose tackle aligned head up on the center (0 tech) and two tackles aligned head up on the offensive tackles (4 tech).
Now, other players can be added to the line of scrimmage to create a five front look, and this may cause some of the DL to bump down a man or two, but in essence, it's the same thing.
3 Front and Gap Responsibility
Typically, a 3-front defense is a two gap type of scheme. What that means is you're required to read and react to close the gap to the playside. You have keys in the offense, most notably the offensive linemen in front of you. If a guard pulls, he's going to bring you to the football the majority of the time. If the offensive lineman pass sets, you're probably going to rush the QB (unless a blitz is on, then responsibility CAN change to an occupier role). But the bottom line is, they have to make a read and react. The nose, for example, will attack the center and slide into a gap as a play develops. Some of the best noses don't have to engage and react, they can react at the snap because they see what's going on. They are responsible for both A-Gaps technically.
However, a 3-4 scheme doesn't HAVE to be a two-gap scheme. It can be played as a one-gap defense, it's just not as common as the two-gap.
An A-Gap is the gap to either side of the center. The B-Gap is the gap between the guard and tackle, C-Gap is between the tackle and tight end and the D-Gap is outside the tight end, or where the TE would be.
I'm not going to go into too much detail here, instead, I'll link you to jtyler42's post in the Random Chalk Talk Thread, he really touches on the minute differences of the 3-4 defenses very well:
The 4-3 is an even front defense. An even front uses a nose tackle (except here he plays more of a 2 technique, or for simplicity's sake he aligns himself on the inside shoulder of the guard). The defensive tackle will align in a 3 technique (outside shoulder of the guard), and then you usually have a 5-tech defensive end to the nose side and another end anywhere between the 5-8 techs dependent on if there's a tight end. The side of the line with more offensive lineman, or the strong side, is the side where you'll see that 3/5-8 tech defenders.
There are many variations to the 4-3 defense.
The 4-3 under defense and the 4-3 over defense are two of these variations. There are cases, such as Nick Saban's "Bubble Over" defense.
The Mike will declare the strength, or as Saban likes to call it "The Bubble Side" (away from the TE). The Will walks up to the outside of the line of scrimmage, next to the offensive tackle or tight end (making it appear to be a 3-4 defense). To add to the illusion, the nose tackle will shift over and play a 0 tech, also mimicking what teams do with a 3-4 and the DE to the strong side will sometimes stand up, leaving you with 3 "down" lineman and four "backers". This player is generally in a 9-tech (outside shoulder of the tight end) and the tackle to that side lines up in the traditional 3-tech.
To the side with the traditional even front lineman, they play a 1-gap system. So the strong side DT and strongside end will all play single gap. The other side will be played as a 2-gap defense, that would be the weak end, and the nose.
The 4-3 Under is a scheme that generally assigns the Sam to the TE. The rest of the line will kick down a bit. The strongside defensive end will play a 5-tech, the strongside tackle will play a 0-tech (resembling a 3 front nose tackle), the weakside tackle will play a 3-tech and the weak side end will play a 6-tech (outside shoulder of the tackle).
In this D, the 0-tech and the strong end play 2-gap defense and the 3-gap tackle and the end play a 1-gap scheme.
If the tight end motions across, usually the Sam will go with him.
Again, these are only the basics, and I wish I had diagrams of these defenses