Continuing the NNFBG series today we take a quick look at the common defensive schemes played in the NFL as well as pass coverages.
Obviously there are base defenses, referred to as such because they are played more snaps than any other, and also sub-packages. Coverages can overlap any defnsive scheme and are simply the responsibilities of the players in covering receivers in the pass-game.
The two systems employed as a base defense in the NFL are the 4-3 defense and the 3-4 defense. The numbers indicate how many defensive linemen and how many linebackers there are, in that order. If you remember a previous post in the series about DL alignments, that will tell you more about the differences for the linemen.
In general a 4-3 defense seeks to penetrate and disrupt plays behind the line of scrimmage. Conversely the 3-4 seeks to plug up lanes and give ball-carriers nowhere to go. Of course if the players read a pass, they won't just sit there and clog a lane, rather they'd at least attempt to get to the quarterback...albeit some of these big nose-tackles don't generally get a lot of sacks.
After the jump, a bit on sub-packages and coverages.
There are a variety of sub-packages that are employed usually when the offense brings uneven personnel on the field, such as extra linemen and tight ends for short-yardage situations, or extra receivers for passing downs.
Goal-line is usually what's known as the short-yardage package, and often includes five or more linemen and fewer defensive backs.
Pass packages are usually named by a monetary unit, ie. "Nickel", "Dime", "Quarter", and "Dollar". The unit increases in relation to how many defensive backs are on the field. Nickel means five defensive backs (usually three CB's and two safeties, but can be reversed). Dime is six DB's, Quarter is seven, and Dollar is eight.
As you can see, defensive formations are all about personnel on the field. Their responsibilities vary, even within each formation. As said, coverages are about responsibility in the passing game as it pertains to receivers. The two basic principles are:
Zone Coverage: Players guard areas, rather than follow one specific offensive player wherever he goes. Any throws to their "zone" are to be broken-up before a reception is made, if possible, or at the very least an immediate tackle must be made.
Man Coverage: Also known as "man-to-man", this is where each player has an opposing player to shadow, following him wherever he goes until a throw is made elsewhere. Their responsibility is the same in terms of preventing a reception or making a tackle, but they are in closer proximity (if they don't get beat) to their player, usually.
The coverage schemes within these are numerous, but here are the basics:
Cover-2: The CB's cover a shallow area just beyond the line of scrimmage from where they line-up, usually anything from the sideline-in. The safeties take the "deep halves" of the field, dropping back and playing zone on their side of the field. Linebackers usually occupy the middle of the field in the intermediate area. A variation of Cover-2 is Tampa-2, which sees the MLB run the deep center to help the safeties not have to cover such a wide area.
Straight-Man: Also called "Cover-0", Everyone plays man-to-man on a specified player. There is no "help over the top" in this coverage from the safeties, who are usually covering tight-ends and running backs...often on short-to-intermediate routes. If a CB get's beat by his man on the outside, it's likely to end up a very long gain.
Man-Free: Also called "2-Man", this means that the CB's and LB's play man-to-man but the safeties play 2-deep zone over the top, as they would in a Cover-2. Putting a bunch of receivers on the field would negate this coverage as there aren't enough athletic cover players on the field to match-up with them, and a player can easily find an open spot in the short-to-intermediate areas.
Cover-1: One single deep safety plays zone and everyone else is in man-to-man. You'll notice that "Cover-X" refers to how many deep zones there are. It should be noted that the deep zones can be occupied by CB's, and often are. Sometimes the safeties come up and play underneath while the CB's drop back into the deep zones.
There are many exotic variations and these formations and schemes are constantly evolving. Those are the basic, though, and I hope you find it helpful.