From junior high on up, this is the most basic scheme. Cover 3 explains itself, it is three DB's with deep 1/3 responsibility. This means these three DB's are in zone coverage, and by no means can they allow a receiver to get behind them. In it's simplest form, if the ball is snapped in the middle of the field, and the formation is fairly symmetrical, the outside DB's (usually cornerbacks) will cover the area from their sideline to the hashes, and the middle DB (a safety) will cover the area between the hashes. Their "zones" will normally begin at about 15 yards deep, and their responsibilities will extend to the back of their end zone.
Each DB's alignment depends on their speed and the receiver's speed. The faster the receiver, the deeper the DB's initial cushion. The outside DB's are usually aligned one yard outside the No. 1 receiver (the receiver furthest from the ball). This allows them to look into the offensive backfield, while still keeping an eye on the receiver in their zone. The middle DB usually splits the difference between the two outside DB's.
Zone coverage means each DB covers an area, not a man. So on crossing routes (a receiver running across the middle), the DB's need to communicate, passing the receiver off to the DB in the next zone, and looking for another receiver to enter their zone. On rollouts, or "boots" (play action one way, the QB reversing and rolling out away from the flow), these zones need to be adjusted to the flow of the QB and receivers. If two receivers are in the DB's zone, he needs to split the difference between the two receivers, reading the QB's eyes. It is best to shade the receiver closer to the QB on two vertical routes, forcing the QB to make the longer throw. This means the ball will be in the air longer, allowing the DB to make the play.
In a fairly vanilla scheme, the linebackers (or the fourth DB, or the nickel back, etc.) will be responsible for the short zones (zero to 15 yards). The same zone principles apply, and these defenders will deal with more crossing routes. Of course, if they are still within five yards of the line of scrimmage, nothing makes things easier on a defense than a LB knocking a receiver off his route, or even better, onto his rear-end.
Strengths of Cover 3:
This is an easy coverage to implement. Three players play pass first, run second, the front eight players play run first, pass second. Having three deep players SHOULD take away the deep pass. We all know better, but that is the plan. Against poor throwing teams, the DC (defensive coordinator) is playing the odds, betting the offense will make a mistake before they are able to move the ball down the field for the score. Against multiple formations and motions, this isn't the best coverage, but it is the usual audible if players are confused, as it is the easiest to play.
Weaknesses of Cover 3:
This is usually a fairly passive scheme. There are exceptions to this, but for the most part, this coverage screams out "bend but don't break." Good QB's and receivers will find the holes in the zones, and if they're on their game, you can count on the defense bending. In a vanilla Cover 3, sending an additional player to rush the QB either means giving up a zone (scary, but sometimes effective), or spreading your underneath coverage very thin, making the seams between the zones bigger. An offense can also create an advantage by "flooding" a zone. This term describes a combination of routes attacking a zone or zones with more receivers than defenders in that area. Most great QB's will tell you, this is their favorite coverage to attack. Also, as easy as it sounds, playing zone defense is more difficult for many DB's. Experience is the key, the more familiar a DB is with his responsibilities, and the more plays he sees, the better he will play his zone.
Many teams use different terms for this coverage, but it is football in its simplest form, all the way back to the sandlots: "You have that guy." By that I mean "man to man" coverage. Many teams call it Cover 0 as a friendly reminder to each DB that you have zero help behind you. It's just you and the receiver; God's speed, good luck. The philosophy is simple, the athleticism required is another story.
While various formations and stunts will determine each player's responsibility, in its most basic form, each outside DB (corner) will cover the #1 receiver to his side, and the safety or safeties will cover the #2 receiver to his side.
Most teams will teach their players to align on the inside shoulder of the receiver, or one yard inside in man-to-man coverage. Taking away the inside route is very important, as it is a shorter throw for the QB, and a quick slant can become a quick TD very quickly. Once again, the speed of the receiver and the speed of the DB determine how much cushion the DB will allow with his initial alignment.
If the receiver goes in motion across the formation, the DB's will either bump down, exchanging responsibilities, or more likely simply run across the formation with the receiver. This is why many teams use motion, to see if the defense is covering man-to-man or zone.
Running backs out of the backfield, or additional WR's in multiple receiver sets, are covered by the nickel back or linebackers. Thus the match-up problems OC's (offensive coordinators) love to exploit. Note: Good OC's are evil people, and will pay for their sins in the afterlife.
Strengths of Cover 0:
Pressure, pressure, and more pressure. Playing true man-to-man frees up the the largest number of available rushers to get after the QB. Pressuring the QB can lead to turnovers, sacks, and incompletions when the QB is running scared. Remember, the philosophy of the '85 Bears was "let's see how good the second string QB is". Punishing the QB can win games. The DB's also aren't asked to cover their respective receivers as long, as the QB better be on his back after a few seconds.
Weaknesses of Cover 0:
A good QB in a sophisticated passing offense can hit his "hot reads" (alternate, shorter routes to counteract a blitz) and torch this coverage. Sorry Bears fan, think Marino on Monday Night in '85. It also requires amazing athleticism from the DB's, as they are "Gilligan", which means all alone out on an island. As much as I dislike his playing style (hate is such an ugly word), Deion Sanders was perfect for this coverage. Coach Weis and Brady Quinn had a field day against BYU this year due to their non-stop blitzing. Crossing routes are often called by the OC, in the hope of "rubbing" defenders off as the receivers cross. This can also be defined as a "pick" play, but we all know that is illegal and no OC would ever think of bending the rules (never). Also, man-to-man coverage against a mobile QB can lead to a short career for a DC. If the DB's are turning and running with their receivers, and a QB manages to avoid the blitz, he can run for miles before any DB's realize he's taken off as a runner. A "spy" (a DB or LB who is responsible for shadowing a mobile QB) is normally used to discourage the QB from running, and punishing him if he chooses to do so. Screen passes can also be used to discourage the blitz, capitalizing on the defenses' aggressiveness. It's all a chess match.
Cover 1 is exactly like Cover 0, except one DB plays Free Safety (FS), helping out "over the top". The FS's job is to take away the big play, and ball hawk any poor throws that result from the pressure the QB is facing. An experienced FS can make all the difference. God loves a good FS (I believe I've mentioned this before).
Film study by the FS is incredibly important. The quicker he reads the play, the quicker he can alert his fellow DB's. Whether it is a screen, draw, downfield pass, or QB scramble, having one DB looking into the backfield is a big help to the other DB's playing man-to-man coverage. Communication is once again very important.
Strengths of Cover 1:
Cover 1 allows the DC to still be very aggressive in his play-calling. And having at least one good athlete playing deep allows the DC to sleep better at night. At the high school level, the discrepancy of athleticism from player to player makes this easier to play. Having one superior stud able to roam the field is a nice security blanket.
Weaknesses of Cover 1:
Very similar to the weaknesses of Cover 0. However, as mentioned above, at least one player is playing deeper with his eyes in the backfield.
Up next: Cover 2 and Cover 2 Invert