How did New England find the right combination of offensive linemen this season, and where are Seattle's biggest weaknesses in pass protection?
15 Aug 2005
by Mike Tanier
There are as many different variations in zone coverage as there are defensive coordinators at the pro, college, and prep ranks. This article is an overview of some general terms, rules, and concepts that are used by coaches at all levels. Before reading on, you may want to check out Chris Miraglia's article about the Cover-2 defense; we'll touch on some aspects of the Cover-2 here, but this essay focuses more upon Cover-3 rules, terms, techniques and assignments.
Zone coverage schemes are usually named after the number of defenders assigned to the deep zones. The Cover-2 is a two-deep zone, usually meaning that two safeties are responsible for deep routes. The Cover-3 is a three-deep zone. The Cover-4 is often called "Quarters" coverage because four defenders each handle 1/4th of the deep part of the field.
What about Cover-1? That's man coverage with a deep safety. No defender can control the entire deep part of the field by himself, so any time there's a single deep safety, other defenders will have to run with their receivers, hence creating man-to-man responsibilities.
And five is right out. Teams may use something akin to a five-deep zone against Hail Mary passes at the end of a half, but it generally isn't called a Cover-5.
Terms like Cover-2 designate the deep coverage, but many coaches will also refer to the underneath coverage when explaining a play. In Miraglia's explanation of the Cover-2, he diagrams a two-deep, five-under defense; some coaches call this a Cover-7 to denote the seven players who stay back in pass coverage. A typical Cover-3 defense includes four defenders underneath, while a quarters defense usually has three players in underneath zones.
Of course, the numbers change when a defense blitzes. Blitzers come from the underneath zone coverage, forcing their teammates to defend larger swatches of turf. As Miraglia points out, coaches like Tony Dungy don't blitz frequently out of their Cover-2 schemes. But coaches like Dom Capers and Dick LeBeau like to blitz from the Cover-3. Often, they'll send two players to blitz, leaving three defenders in the underneath zones (both coaches use a 3-4 alignment that gives them an extra linebacker to play with). That's the typical zone blitz: three deep defenders take away the big play, while five pass rushers force the QB to pass quickly.
Just who plays deep in a three-deep zone? In "sky" coverage, the two cornerbacks and a safety cover the deep zones. In "cloud" coverage, one cornerback and two safeties handle the deep part of the field. That is sure to answer a question for some Madden and NCAA Live gamers, who often see the words "sky" and "cloud" used without explanation to denote defensive plays.
Cover-3 systems leave one player in the secondary free to either blitz or defend an underneath zone. Even if the extra safety or cornerback doesn't blitz, he can still step up and occupy a zone just vacated by a blitzing linebacker. Coaches then have incredible flexibility when disguising coverage, or when rolling the defense.
"Rolling coverage" means shifting the defense after the snap to provide extra support on one side of the field or another. In a cloud coverage scheme, the defense will often roll in the direction of the one cornerback who is not responsible for a deep zone. One safety shifts to a position behind that cornerback. The second safety moves to the middle of the field. The other cornerback drops back. A linebacker slides into the flat in front of the deep cornerback. Throw in a blitzing linebacker (with a cohort shifting into his zone) and the quarterback's read is very difficult: it's hard to tell who is responsible for which zone, and defenders suddenly appear in what should have been soft spots on the field.
Coverage is rolled for a variety of reasons: to protect a rookie cornerback, to provide extra support against a top receiver, or to help disguise a blitz. Coaches can cause further confusion by varying the size of the zone covered by each deep defender.
In a Cover-2 system, the two deep safeties (or, often, one safety and one cornerback) are each responsible for about half of the field. In a Cover-4, the deep part of the field is generally sectioned into four equal parts. But in a Cover-3, coaches have some flexibility.
Usually, the deep part of the field is broken into three equal parts. But coaches can also design quarter-quarter-half schemes: two deep defenders are only responsible for 1/4th of the ground, while the third must take care of half the territory.
When Randy Moss lines up on the right side of the field, the opposing coach may be tempted to call quarter-quarter-half, with both a cornerback and a safety shifted to deep coverage on that side of the field. For quarterbacks who like to roll out or who prefer to throw to one side of the field, quarter-quarter-half coverage provides extra support on the side of the field that the offense is most likely to attack. In college football, where the hashmarks are further apart and the arms are weaker, the "half" defender can sit back and worry about difficult across-the-body passes while two teammates handle more likely pass targets.
Quarter-half-quarter coverage is also possible: typically, the two cornerbacks deal with 1/4th of the field near the sidelines while a rangy safety handles the deep middle. When the opponent likes to throw lots of fade passes, fly patterns, and sideline routes, quarter-quarter-half coverage can force those pesky receivers to come across the middle.
There are theoretically three seams in a two-deep zone. One begins about 14 yards down the middle of the field, extending to a depth of about 20-25 yards. The other two are at the same depth along the sidelines. These seams lie behind the underneath coverage but between the safeties (or the safety and the sidelines).
In reality, that middle seam is disappearing at the pro level. Safeties and linebackers are so fast that someone is going to converge on that 18-yard pass over the middle unless the offense puts some effort into creating some space. For example, one receiver could run a deep post, forcing a safety to drop back and allowing a second receiver to enter the seam a split second later. The sideline seams are still common attack points for the offense, but 20 yard passes along the sidelines aren't easy to execute.
A Cover-3 zone has two seams. Each begin about 15 yards from the sidelines and are about three yards wide. Like the seams in a Cover-2, these seams extend from a depth of about 14 yards to one of about 25 yards. When you hear that a tight end or slot receiver ran a "seam route", it means that he ran a simple fly pattern into one of these hard-to-get-to cracks in the defense.
In addition to the seams, zone defenses have a no-cover zone. This is a three-to-five-yard zone extending out from the line of scrimmage and running the width of the field. No defender is supposed to cover a receiver (usually a running back) who is sitting in the no-cover zone.
Does this mean that zone defenses are meant to allow an endless stream of three-to-five yard passes? Not at all. Underneath defenders are expected to read the quarterback, anticipate the throw into the no-cover zone, and beat the ball to the receiver. If the defender jumps the route and picks off a pass, he could easily score. He's in good position to tip the ball even if he doesn't intercept the pass. At worst, he can make a tackle for a four-yard gain. Had the same defender camped out in the no-cover zone with his receiver, his zone would be stretched thin, and he would be vulnerable to a move up the field.
If you ever tried to play a zone defense in a pickup game, you probably realized right away that it's hard. In basketball, setting up a 2-3 zone is pretty simple: the space is limited, so it is pretty easy to pick up guys in your zone. In football, with all of that space, you may find yourself defending an empty patch of turf while receivers catch passes in front of you, next to you, and behind you.
Rams fans can relate. Their young linebackers had a hard time with the intricacies of zone coverage last season, allowing lots and lots of receptions by tight ends and running backs. It wasn't that Robert Thomas and company weren't fast enough to stick with their receivers. Rather, the problem was that they were too inexperienced and indecisive to read and attack pass routes.
That brings us to the key element of zone coverage: defenders must break on the ball before the pass is thrown. Any defender who sits in his zone and waits for the quarterback to release the ball before making his move is a cooked goose. He must watch the quarterback and follow the progression of the pass routes in order to determine where the pass is going to be thrown, and he had better be moving when the ball is released.
Remember that zone coverage is not man coverage: a linebacker assigned to the "hook" zone (the region about 7-10 yards from the line of scrimmage just outside the tackles) cannot rush out to blanket a tight end who enters his territory. If he does, he'll be in no position to stop the running back executing an angle route into the same zone or the wide receiver running a slow drag from the other side of the field. All three players will be that linebacker's responsibility at some point in the play, so all he can do is drop into his zone and stay alert.
That means that the tight end could run an eight-yard pattern, curl to face the quarterback, and stand there with the linebacker six yards away. Essentially, the tight end is open, because the linebacker is on the lookout for other receivers. If the quarterback decides to throw to the tight end, the linebacker has to beat the ball there. That only can happen if he anticipates the pass.
But how can defenders perform these nearly psychic readings? They watch the drop of the quarterback, knowing that shorter drops lead to shorter passes. They read his eyes. They watch the cock of the shoulders: longer passes require the quarterback to dip his back shoulder. They learn the difference between a passer's pump-fake and his throwing motion, and they look for clues, like patting the ball, that indicate that the quarterback is ready to release.
The pass routes themselves provide further clues. Offenses use routes in combination to beat zones. That eight-yard curl by the tight end is often accompanied by an angle route or flat route by a running back, with a deep post route by the receiver on that side of the field. A savvy defender can figure out what the defense is up to and follow the same reads the quarterback makes.
All of this reading and reacting requires a lot of gray matter. It's an oversimplification to say that man coverage is all about athletic ability, while zones are all about intelligence. But there is more than a bit of truth in the statement. Excellent athletes have proven to be hopeless in zone coverage because they don't react quickly (Derrick Gibson of the Raiders is an example), while slower defenders with tons of experience can be very effective.
The basic mathematics of football hasn't changed in decades. There are five eligible receivers on offense. Assuming that the defense reserves five players to cover them (in man or zone), that leaves six free defenders. At least three will rush the passer, probably four. That leaves two free hands.
Those free players can blitz. They can drop into zones. They can double cover receivers. They can rotate, rushing the passer while a lineman drops into coverage or sliding into a deep zone while a cornerback blitzes.
The defense can play two-deep, five-under, chocking out the short passing game. It can play four-deep, three-under, a great defense for a two-touchdown lead in the fourth quarter. It can play Cover-3 Cloud, with a cornerback and linebacker blitzing, a defensive end dropping into a flat zone, and the secondary in quarter-quarter-half responsibility. Or they can man-up, let the free safety roam, and send one linebacker on a blitz.
The only limits to the variety of coverage types are the imaginations of the coaches and the physical limitations of the players: Hollis Thomas can't drop into a deep zone. Essentially, anything is possible. That's why quarterbacks spend hours breaking down film, and why players on both sides of the ball have to be a whole lot smarter now than they used to be.
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