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Football 101: Pass Coverage

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Football is a complex sport on any level. On any play, there are millions of factors that determine the success or failure of either side, but the best thing about football is that it’s competitive. That’s what keeps people watching. Both teams are trying to win the game, and the success of the winning team is based solely on its performance. On any level of competition, the biggest contributing factor to victory is talent. In the modern NFL, every player has talent and most have played football their entire lives. Typically, games in the NFL are very close, and most teams are well matched in talent. Therefore, the factors of game-planning and execution have become more important than ever. On defense, game-planning is basically refining their defensive coverages and tailoring them to their current opponent, and good execution starts with practice and ends with coaches putting their players in positions to be successful. 

Football fans have heard the terminology and typically have a good understanding of basic defensive strategy. The idea is to keep the other team from scoring. On run plays, the defense needs to tackle the ball carrier and would like to do so behind the line of scrimmage. On pass plays, the defense needs to cover the offense’s receivers long enough to pressure the quarterback into a bad throw or sack. That’s the great thing about football. Even the casual fan can determine if the offense or defense is achieving its goal on a given play. However, anyone who has played football on any level will tell you that there’s more to it than simply lining up and throwing a ball around. On defense, players must learn to anticipate and react to the offense’s plays. Even more than that, they must learn to work together as a unit. Good offenses will try to force and exploit mismatches in the defense and will use all eleven of their players to do so. Therefore, the defense must work together if they want to have any hope of success. 

Whether it’s a run or a pass, defensive strategy starts up front with the defensive line and the pass-rush. Before the snap, the defense doesn’t know if the offense will be running or passing to advance the ball but can anticipate what the offense will try based on the game situation. This seems like an obvious point, but it is a huge factor in how defenses call plays and prepare. First, all defensive plays must have a plan for the running game. If the quarterback hands off the ball, all defensive players will converge on the ball carrier as quickly as possible, and coverage responsibilities are forgotten. There is strategy in run defense, but we’re only going to consider pass coverage in this article. Second, all defensive plays must have a plan to cover the pass if the quarterback doesn’t hand-off the ball. The ideal defensive achievement on a pass play is to tackle the quarterback immediately after the snap. Since the quarterback has an offensive line blocking pass-rushers for him, that rarely happens, and the defense needs to prevent the offense’s receivers from getting into a position to catch the ball long enough to allow the pass-rush to reach the quarterback. If the ball is thrown, the defense needs to prevent the receiver from catching it. As one can imagine, those goals aren’t easy to achieve, and over time, defenses on every level have developed many creative coverage methods to stop offenses from passing the ball.

Now that we understand the objectives, what actually goes into defending against the pass in modern pro-football? In general, most teams execute the same basic principles in defense and use those principles to create their overall defensive scheme. Defensive schemes are based on the athletic strengths of the team’s personnel, and the complexity and depth of those schemes are based on the football intelligence of the team’s personnel. Most modern defensive schemes are very complex, and there isn’t a single professional team that runs the same play over and over again. Most teams will use multiple coverages throughout the course of a game. Those coverages are based on the following three basic defensive assignments: zone coverage, man coverage and blitzing. In this article, we’re going to analyze those defensive assignments, what makes them successful, their weaknesses and how defenses implement them into modern coverage schemes.

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Zone Coverage [Figures 1, 2 & 3] 

All pass coverage breaks down to numbers. On the offensive side, there are five offensive linemen and the quarterback. The five offensive linemen (two tackles, two guards and a center) are not allowed to receive un-tipped passes from the quarterback and are not eligible receivers. The offense can use any player they wish as an eligible receiver, but if an eligible receiver is listed as an offensive lineman on the active roster, he must declare as an eligible receiver before the snap. Since it’s not effective for the quarterback to pass the ball to himself, there are always five eligible receivers on offense, and the defense needs to account for five potential receivers on every play. The personnel that the offense uses as their five eligible receivers can help the defense predict the offensive play. 

The defense can cover those five receivers in a couple ways. One of the most effective ways to cover the receivers is to cover the field where the receiver wants to catch the ball. That principle is called zone coverage. The average pass rush in the NFL consists of four defenders. That leaves seven players to cover five receivers on the average play. The idea behind zone coverage is to use those defenders to flood the field and cover the zones where the quarterback wants to throw the ball. Since there are more defenders in coverage than receivers running routes, there should always be a defender to cover a receiver no matter where he runs on the field. Theoretically, this principle works. The only problem is that NFL quarterbacks are extremely accurate with their passes and defenders that are backpedaling are often caught out of position. The other problem is with the principle of zone coverage. Every defender needs to defend his zone, and as a receiver is transitioning from one zone to another, there is usually a gap in coverage. These gaps are referred to as "holes" in the zone coverage, and the passing accuracy of NFL quarterbacks allows offenses to exploit the holes if the quarterback can read the coverage.

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When using any form of zone coverage, the defense must divide the field into zones and choose which zones to defend. Since the defense is trying to stop the offense, it only makes sense to divide the field based on offensive strategies. That’s exactly what most football teams do. There are many different terms for the zones, but the basic principles remain. The defense wants to put most of its defenders into the areas where the offense is most likely to throw the ball. Coaches often talk about "high-percentage" passes and plays, which have a high percentage of being completions. Since it’s harder to throw the ball accurately deeper down the field, the high-percentage passes are typically short passes. Therefore, the defense will often put more defenders into short zones, and the field is typically divided into smaller zones closer to the line of scrimmage. The zones closer to the line of scrimmage are typically referred to as the "underneath" coverage, and the zones further from the line of scrimmage are typically referred to as the "over" or "deep" coverage. Furthermore, defensive plays are identified by the number of players in deep coverage. For example, a play with two defenders playing deep zone coverage is referred to as "cover two," and a play with no deep coverage is referred to as "cover zero." 

The field is typically visualized in the following eight zones by coaches and players: two flat zones, two middle or hook/curl zones, two out zones and two deep zones [Figure 1]. The deep coverage can be split into 1-4 different zones, but it’s typical to view it in halves. Passes to the flat zones are considered the highest percentage passes, and the flats are generally exploited if a defense gets either too soft or too aggressive. The middle zones would seem like the easiest place to throw the ball since they’re directly in front of the quarterback. However, the massive defensive linemen pressuring the quarterback and the linebackers in the middle make the middle of the field a hard place to fit in a pass. The out zones are one of the harder zones to cover and will stretch a defense if the offense forces them to be covered. The hardest part about completing passes to the out zones is the arm strength required from the quarterback. Throws to the out zones need to be hard, straight-line throws since the window where the receiver is open is small, and since the throw is diagonal to the line of scrimmage, the in-air distance of the ball is long compared to the length of the completion. The deep zones are to prevent the quarterback from throwing the ball long and ball carriers from scoring if they make it past the underneath coverage. Since there are eight zones and the defense will often put more than two defenders deep, the defense cannot cover every zone and needs to choose which zones to defend. 

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The cover three defense [Figure 2] is a very common defense in the NFL. The underneath coverage can vary, but with a four man pass-rush, four defenders remain in underneath coverage. The linebackers and strong safety are used to defend the underneath zones, and the free safety and corners are used to defend the deep zones. Since there is only one defender covering the deep center of the field, this coverage will often rely on the inside linebackers to get deeper in coverage. The best feature of the cover three defense is that it covers the pass evenly while providing an excellent force against the run. The corners ensure that speedy wide receivers will not make it past them. Also, the pass rush can be multiple in a 3-4 scheme since the fourth pass rusher can be any member of the underneath coverage. An athletic free safety greatly increases the cover three defense’s effectiveness. That allows the safety to cover more field from sideline to sideline or disguise the coverage by lining up close to the line and faking the blitz. The weakness of the cover three is covering the seams, the straight lines between the free safety and corners. This weakness can be covered up with a smart free safety, but if the safety makes a wrong read, it could leave a corner in deep, one-on-one coverage, which can often lead to long completions. 

The cover two defense [Figure 3] focuses on the underneath coverage more than the cover three defense. With a four man pass-rush, the cover two defense has five defenders in underneath coverage. Like the cover three, the fourth pass rusher can be any member of the underneath coverage in a 3-4 scheme. One advantage of the cover two is that the wide receivers can often be "bracketed" or "double-covered." Since the corner is covering the flat, he can jam his receiver at the line and stay directly in front of him if no other receivers move into the flat zone. This allows the wide receivers, who are usually the fasted and most talented pass-catchers, to be covered underneath by the corners and deep by the safeties. Obviously, it is extremely hard to have any success with short throws or throws to the wide receivers against the cover two. The largest weakness is in deep coverage. The cover two is extremely liable to the deep, center-field seam-route, and if a quarterback reads the defense pre-snap, he will often change the play to take advantage of that weakness. 

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Man Coverage [Figure 4] 

Man coverage is much simpler than zone coverage, and the principle of man coverage is different than zone coverage. When you assign a defender to man coverage, you are simply assigning him to cover one receiver. The objective is for the defender to stay close enough to the receiver that the quarterback will not throw the ball, and if the quarterback throws the ball, the objective is to break up the pass or intercept the ball. That sounds easy enough, but man coverage is much riskier than zone coverage. This is because most routes that receivers run are specifically designed to shake man coverage and gain separation from the defender. In man coverage, separation by the receiver usually equals a reception. Furthermore, the receiver could just out run the defender to the end-zone if the receiver is faster than the defender covering him. 

The principle of man coverage is different than zone coverage for two main reasons. First, the personnel required to successfully run either coverage have opposite attributes. Speed and athleticism are two of the most important attributes for a defender in man coverage, and intelligence and anticipation are the most important attributes of a zone defender. That’s not to say that all of the attributes aren’t beneficial in either scheme. Second, zone coverage buys time for the pass-rushers to get to the quarterback by covering the receivers, but man coverage shortens the time that the defenders need to cover by bringing extra pass rushers to hurry or sack the quarterback. 

The cover one defense [Figure 4] is a great example of how man coverage based defenses add defenders to the pass-rush to take pressure off the defenders in man coverage. The cover one defense has a defender assigned to every receiver. Since there are eleven defenders to cover five receivers, that leaves five defenders playing man coverage, one defender in deep coverage and five defenders to rush the passer. The objective is to disrupt the quarterback as quickly as possible. The defenders can jam the receiver within five yards to further disrupt the timing of the offense. However, the offense can get a large gain if the pass rush doesn’t reach the quarterback or the coverage men allow their receivers to get behind them. Obviously, it’s a risky scheme, but with good personnel, a man-coverage, heavy-blitzing defense can be suffocating. History has shown that some of the best defenses have been these types of defenses. 

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Zone Blitzes [Figure 5] 

Zone blitzes are a way to take the safety of zone coverage and mix it with the pressure of man coverage. As you can imagine, that’s a very effective combination. Zone blitzes were developed by the hard charging defenses of history like the old Steelers defenses and the old Patriots defenses. I’d love to be able to give the credit to our Ravens, who run zone blitzes as successfully as any team right now, but zone blitzes have been around for a while. Now, every team in the league has a highly developed and complex zone-blitzing scheme. 

Zone blitzing incorporates all of the principles that I talked about above. The most important thing to realize about zone blitzes and all defensive plays in general is that they aren’t restricted to strictly zone coverage or man coverage. The defense can run any variation or combination of coverages that they want. In fact, it’s very common for defenses to run zone-man coverage combinations. To understand defenses, one must understand the numbers of the defense. If the defense sends five defenders to rush the quarterback, that leaves six in coverage. The defense can then use the six defenders to cover based on the game situation. They can man cover the wide receivers and leave the remaining four defenders in zone coverage, or they could simply play a cover three defense with three underneath zone defenders [Figure 5]. The point is that coverages are extremely multiple in pro football, and even though most schemes will have a base defense, all defenders are expected to be flexible. The defense that isn’t flexible and multiple will not be effective. 

The Ravens Defense 

Over the last decade, the Ravens have consistently had one of the best defenses in the NFL and have always had great coverage schemes. However, they have undergone several scheme changes, so the key to their success obviously isn’t a single defensive scheme. The Ravens are successful because they consistently find ways to play to the strengths of their personnel. In a time where most defenders are on the same level and teams have a hard time keeping their star players due to free agency, the best defensive schemes make the most out of their average players. The Ravens find average players with a single dominate trait and make those players into role-players on the team. In this way, the collective talent of the entire team is increase because every player is playing to their strengths. 

The Ravens do have a huge wild-card when it comes to pass coverage. Ed Reed is one of the best pass defenders in NFL history. Reed helps the Ravens in many ways on defense, but he makes his biggest effect is as a center-field defender. Having Reed is basically like having an extra player in the secondary. His preparation, anticipation and athleticism allow him to cover receivers that would be outside the range of most players. Reed can also disguise coverages better than any safety in the league. He routinely drops down into the box even when he is assigned deep, center-field coverage. This confuses opposing quarterback, whose pre-snap read tells them to throw the ball deep. A perfect example of this occurred in the 2008 playoffs

The Ravens defense has been developed around man coverage on the outside and pressure to force the pass. They have drafted and signed personnel to fit this scheme. Therefore, they will not be successful when they struggle to put pressure on the quarterback. The 2009 season was a prime example of this fact. The Ravens corners are not good in zone coverage and have received criticism this offseason. After re-watching every game last season, the reason that the corners struggled early last season was obvious to me. They are terrible in zone coverage, and the Ravens were using zone coverage early in the season. The Ravens corners do not have good anticipation, are easily fooled with hip fakes and with the exception of Webb, are not very good in run support. Those factors led to them being out-runned, out-jumped and ultimately, overmatched. Now, I’m not saying that they’re bad corners. I’m saying that they’re bad zone cover corners. When they were allowed to play man coverage, they actually did quite well. They’re all smaller players, so they’re going to be out-jumped sometimes, but as a general rule, the Ravens corners consistently covered their receivers in man coverage last season. This is cause for some optimism because we should be able to expect the same success next season since the Ravens ended last season allowing their corners to play man coverage. Ultimately, the Ravens defense, like all successful defensive schemes, is most successful when they play to the strengths of their players.

Additional Reading:

Smart Football: Understanding Coverages.

ESPN: The Zone Blitz.

The opinions posted here are those of the administrator of this blog and his loyal readers. They are in no way official comments from the team, and should not be misconstued as such, even though he thinks he could do just as well or even a better job!

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