Editor's note: As architect of Texas A&M's Wrecking Crew defense (1989-93), Notre Dame defensive coordinator (1994-96) and head coach of the Irish (1997-2001), Bob Davie has been recognized as a top X's and O's coach. This season, Coach Davie will analyze offensive and defensive schemes as part of his season-long course on football for ESPN.com. Each week, he will break out the chalkboard and break down the X's and O's in college football.

Over the past couple of weeks we have had tremendous feedback about the Football 101 column. What we will try to do in the following weeks is answer your most frequent questions. Many of you have had questions in regard to defensive pass coverages and specifically Cover 2. Every defensive football team in the country has some variation of Cover 2 in their defensive package.

This week's class will explain what Cover 2 is, how to play it and some variations. We will also show ways offenses can attack it.

Terminology
Why is it called Cover 2
When deciding the terminology of calling coverages, the number of deep zone pass defenders that are deployed will normally determine what a defensive coach calls a defense. In Cover 2 for example, there are two deep safeties that divide the field into halves. If the secondary played Cover 3, three deep defenders would divide the deep responsibility on the field into thirds. If they played Cover 4, four deep defenders divide the deep zone into fourths.

Obviously, different teams use different terminology, but the most commonly used is simply identifying how many deep zone defenders are used.

What is Cover 2?
The base Cover 2 is a zone defense where every defender is responsible for an area of the field and not a specific man. The field is divided into five underneath zones and two deep zones. The two corners and three linebackers play the underneath fifths, and the two safeties play the deep halves. In the diagram below you can see the field divided into underneath fifths and deep halves.

Cover 2: How is it played?
In Cover 2, it is obvious that the safeties have a tremendous burden and a lot of field to cover. They must get help from the underneath coverage to keep receivers from outnumbering them in the deep zones. There are two critical techniques that can help the safeties. First, the corners must collide with the receivers and flatten out their routes to keep them from running outside freely, which would stretch the safeties. If the wide receivers release unmolested, it is almost impossible for the safeties to get enough width quickly enough to defend the deep pass. The corners are responsible for their outside fifths, which is a shallow area, but they must sink with the receiver until another receiver threatens their zone.

Pattern read: What is it?
As you can see, Cover 2 is a zone coverage, but it is critical that the underneath defenders at times play man-to-man based on the routes the offense runs. This is the second technique that helps the safety. For example, if the wide receiver to the linebacker side releases outside in a position to stretch the safety deep, the linebacker must know that. He then must carry his coverage on the running back or tight end through the deep zone. This is called pattern read, which means based on what pattern the offense runs, man-to-man principles are applied. This is an example of a linebacker making a pattern read. In the diagram, he sees that the receiver (1) releases outside the corner and he knows that he must carry (2) through the seam where the safety will be outnumbered.

Cover 2: How offenses attack it
(1) Four vertical receivers
The first thing an offense will do if they see Cover 2 is see how you defend four vertical receivers running down the field stretching the two safeties. If Cover 2 is not played properly, this is the first place the offense will go and it could result in a big play. In the previous figure, we showed how to defend four vertical by the corners flattening out the wide receivers and the underneath coverage linebackers running with the vertical of the tight end and running back. But it is also obvious by the previous diagram that if the linebackers fail, a big play is possible.

Cover 2: How offenses attack it
(2) High-low stretch vertically on the corner
The next way the offense will attack Cover 2 is to stretch the corners vertically. The most common way to attack Cover 2 is to high-low the corner who has the outside fifth or flat responsibility. The outside wide receiver runs a post-corner route. In other words, he fakes as if he will run a deep route, which freezes the safety, then breaks back outside to the corner. He knows the safety must stay inside and protect his inside one-half and not allow the receiver to cross his face (which means getting inside of him). The corner tries to sink and help defend the hole between he and the safety to his outside. The offense will then release a tight end or running back into the corner's fifth to create a high-low stretch.

Cover 2: How offenses attack it
(3) In-Out stretch horizontally on the corner
Another way to defeat cover two is to horizontally stretch the corner and create a void between the corner and either the SAM or WIL linebacker. The offense does this by outside releasing the wide receiver to make the corner flatten out and widen. As we stated before, the corner must jam and widen to keep the receiver from releasing outside and stretching his safety. The offense takes advantage of the corner's technique by making him widen with the wide receiver's release and then sending the No. 2 receiver either tight end or running back into the void or stretched area between the linebacker or corner.

Variations of Cover 2
Man under
The most common variation of cover two is when the defense chooses to play two deep safeties but assign the five underneath defenders to play man-to-man on the offenses five eligible receivers. This is an excellent change up because it looks exactly the same as regular cover two zone to the offense. On the snap of the ball, the offense is confused because they have called their zone beaters but the defense locks up on the man-to-man receivers.

Conclusion
Cover two is an effective coverage because you can assign five defenders to play the underneath zones. This makes the offense have to execute at an extremely high level to be effective. The defense is not allowing much space or easy throws. The vulnerability of cover two is that you only have two deep defenders. Obviously, that leaves a large area for the safeties to cover. To help the deep defenders, the underneath zone players must pattern read the routes of the offensive players to take the pressure off the safeties. The key to cover two, or any zone coverage, is getting a great pass rush with your four rushers. No zone coverage can hold up against a good passing football team if you don't pressure the quarterback.

Q & A with Bob Davie
First of all, thanks for all of the terrific responses and knowledgeable questions this week. Please keep sending in the questions and we'll tackle as many issues as we can this season. Here are a few of your questions regarding the screen pass:

Coach,

Very informative column on the screen pass. I have a question for you, though. What defenses are most adept at stopping the screen? I'm an Oklahoma fan, and I've seen a lot of screens blown up in the last couple of years. I am wondering if the offensive players are missing assignments or if the defensive scheme is killing the screen before it gets started?
Bryan
Oklahoma City, Okla.

Bob Davie: The key is to call the right screen against the right defensive coverage. The slow developing delay screen, thrown primarily to the backs, is predicated on the defense being in zone pass coverage and taking deep pass drops. Another example, the jailbreak screen, is more effective against an all-out blitz or man-to-man coverage where there is separation between the rushers getting up the field and being able to pick defensive backs in coverage. Just like anything in football, it's all about the right call against the right coverage.

While well-executed screens can be great plays and are essesntial to keep a blitzing team honest at all times, I hate watching games where an offense calls the same 1 or 2 screens 10 times each. Perhaps even worse than the redundant play calling, often defenses are still getting burned by the same play the 8th time it is called. What are offenses doing to disguise screens? What elements of screen plays make them more difficult for defenses to adjust to?
Brad Wilks
Athens, Ga.

Bob Davie: I don't think you can really disguise a screen. But what you try to do is through your own self scouting, not call screens on predictable downs and distances. Give defenses teams credit, they study your tendencies and it's imperative that whether it's screens or just another play that you don't get in a pattern of calling similar plays in similar downs and distances.

Coach, keep up the good work. About your column on screens, one effective type is the fake-throwback screen where two or three linemen pull off to the right side and the QB fakes a screen to that side and then wheels and throws to a back slipping out the other way. I have seen this work for big plays. Why don't more teams try this at least once a game?
Seve Jordan
Wayne, Pa.

Bob Davie: I think you bring up a good point -- and it's called the double screen where you actually set up the screen to both sides. I think you're right that you don't see that called as much anymore because it's a high, high execution play. The other thing you don't see called and Florida State used to be good at it, set up the double screen to both sides, get the defense spread out and then delay the tight end and get him the ball. It's another good play.

Send in your Football 101 questions. Bob Davie will answer a few of them next week.