Traditionally speaking, there are two major defensive fronts; an odd front and an even front. The odd front is what we run at West and typically consists of the 3-4 defense-a popular choice by The Patriots HC, Bill Belichick. In the high school ranks the 3-3 stack is becoming increasingly vogue, this defensive front also employs an off front. Even fronts are more common in larger collegiate programs and at the professional level. In high school, they aren't uncommon but the number of backers (4-4, 4-3, 4-2, etc.) and types of personnel within the front change greatly.
For familiarities sake, i'll try and keep this on topic in reference to high school and college. Odd fronts employ a 0-technique NT (0-technique in most systems refers to the position head up over the center and NT is short for Nose Tackle). This 0-tech is used to take advantage of the experience level of a high school center. A center will only ever snap with one hand (although two handed snapping happens its not common-certainly not at the higher levels of competition and rarely at the college level).
We'll use a right handed center for example. A right handed snapper will need to fully commit his right hand to the snap and his off hand (left hand in this example) will have a rubberband type effect during the snap. It will snap up in order to stop the rush of a defensive lineman. In the event of an odd front this will put a NT in the centers grill as soon as the ball moves in even the slightest. A lot of high school centers lack the ability to snap the ball and immediately dominate a block. A good D coordinator can use this to an even greater advantage by using the NT to attack the centers right side. Since the Center's right hand will be commited to the snap the Center will need to cross his body to get his left hand over to slow the rusher, worse case scenario he'll become off balance and lose the LOS before the battle's even started.
We'll address more of the odd front later.
The Even front takes away this immediate threat of the NT/Center but adds a definite rusher by having a fourth man on the Defensive line. This additional rusher can seem like a great idea-following the mantra "more is better", however, an even front takes away blitzing combinations/possibilities and allows an Offensive line to identify another rusher-as opposed to not knowing who will be rushing from an up position in an odd front. Some of the advantages of the even front are; D-line games, pre-snap movement, and one-on-one's.
Defensive line games are crossing stunts or false movements stunts that can be used to mix up blocking responsibilities of the Offensive line. Here's a very simple D-line game that can be effective on a passing down.
This type of a game is even more effective with a stunting Defensive End that possesses exceptional speed. The goal for the End is to get the Offensive Tackle in a retreating state. The Defensive tackle is attacking hard on the inside shoulder of the OT and drawing in the Offensive Guard that he's lined up over. When the OG has been pulled outside with the DT the End will come inside of the gap created by the space. This is called 'splitting the levels'.
This is a simple game but the coaching is very distinct and should be called only during situations and may require some setting up of the offensive line before success is seen. It can be countered with a good center that's able to peel off any inside threat and pick up the End coming inside but that simply adds to the chess match that is football. SIDE NOTE: For those with inquisitive minds, a good DC would see the Center peeling off and would either sugar a backer (bluff a blitz by a Linebacker) or actually blitz a backer.
Pre-snap movement can cause a significant amount of confusion for an offensive line that struggles with adjustments or varies their blocking responsibilities. There are two dominant blocking styles; man and zone. Some more complex schemes can run a variation of zone/man. Both of these schemes can be challenged by movement up front before the snap which takes away the O-lines ability to adjust they're calls and ID their blocking responsibilities. Even the movement of a defender from the outside shoulder to the inside shoulder of an offensive lineman can greatly effect where and how he needs to adjust his blocking. For example, this is the same basic play but because the defense is line up differently blocking responsbilities change. If a D-line were to come out in one look at quickly shift during the snap count the Offensive line may not be prepared to make the necessary adjustments;
One-on-ones are another strength of the even front. With proper technique and coaching faster defensive ends can be placed on the edge and put in charge of coming off of the edge as fast as they can with Offensive tackles being placed on 'an island'. Double teams are primarily used by the interior 3 offensive lineman, Guard, Center, Guard. These 3 are usually less athletic than Offensive tackles and it's the shortest distance between the ball and a defender.
The personnel brought in for these types of fronts can vary a lot depending on the defensive style and philosophy of the coordinator but a common style of philosophy for body types has become prominent through the success seen by Monte Kiffin and his legendary "Tampa 2" defense using smaller defenders (keep in mind that a small defensive lineman in the NFL is still 6'2" 265lbs) with superior speed.
A lot of this changes when referring to the high school level, which can be effected by location, common body styles in the school and area, level of competition, and offensive sets seen. For example, when I played in high school we ran a 4-4 defense because we had smaller bodies with a higher level of speed and played at a smaller level of competition but on the other hand West Linn plays a 4-3 defense at a high level competition and they have the bodies to fill those interior spots and see a lot of passing oriented offensive attacks. The larger bodies at their disposal means they don't have to run a 3-man front [if they don't want too] and rely on LB's or Safeties to rush the passer.
The style of the defensive front that's being used has a rationale behind it and is dicitated by many things. When you watch football, whether it be Friday, Saturday, or Sunday, make no doubt about it there's a rhyme AND reason behind the defensive front. Defensive coordinator position across the nation at many different levels are filled based solely on the type of kids in the program and how they want to use them.
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