One of the more common terms you hear on TV these days or in the print media about defenses is the notion of a Cover 2 defensive scheme. Sometimes you hear it in interchanged with Tampa 2 even though the two schemes are slightly different. Cover 2 defense simply refers to the concept of playing zone defense with five men underneath in coverage and 2 safeties back deep for support. This scheme is a "bend but don't break" type of concept that is used by many teams as a base defense. USC's defense under Pete Carroll uses some form of it maybe on 20-40% of the plays in any given game. Coaches such as Monte Kiffin and Tony Dungy, and Lovie Smith use it as well as a cover shell for initial alignment purposes although they might actually then play something else in reality.
Cover 2 defense is nothing new in the coaching community. It has merely become a fad on TV to mention it since so many teams use it in some form or other. The defense was played by the Pittsburgh Steelers in the 1970's during their championship years and by other teams as well. The notion of having two safeties deep in coverage goes back decades before that as well and was used with a variety of defensive front alignments even in the college ranks.
There are a couple of reasons for the popularity of the Cover 2 defense that I can identify from reading on the topic. The first is that it is an excellent defense in terms of avoiding giving up the big play. With two safeties deep you have a relatively higher degree of support on certain pass routes than on other schemes such as Cover 1 or Cover 3 for example that have only one safety deep. Coaches are adverse to giving up the big play and Cover 2 helps support that goal against both the run and the pass.
Coaches that like Cover 2 generally subscribe to the bend but don't break philosophy of defense. Cover 2 might give up a couple of yards on run plays with only seven defenders in the box until a safety can funnel down for support. Cover 2 also can force a lot of check downs on passing plays when well defended. This forces the offense to earn every yard they gain down the field play after play. It is generally hard for any offense to consistently move the ball down the field on 10-12 play type possession drives. Statistically that long of a drive is quite unlikely to occur more than once or maybe twice per game. The average drive is more like six plays. Third down conversion rates for teams hover anywhere from 30-45% for most teams. Put the opponent in a 3rd down situation enough times and eventually you will force them to punt the ball with those odds working in your favor. Some fans might not like the defense but given its success in the NFL and college level expect to see it around for a lot longer...the odds are in the favor of the team using it.
The other reason coaches have an affinity for Cover 2 is that it lends itself to other coverage schemes quite nicely. Lovie Smith and Tony Dungy acknowledged before the most recent Super Bowl in 2007 that at most their teams actually play Cover two perhaps 30-40% of the time in reality. What else to they do? In a slight shift they might play the two safeties deep in zone coverage and play the five defenders underneath in man coverage. In some cases right before or after the snap one of the two safeties might come down quickly more closely to the linebackers to put an 8th man in the box. Then the corner and remaining safety either play Cover 1 with one safety deep for support or Cover 3 with two corners and the safety deep in zone coverage. On third and long situations both the corners and the safeties might retreat deep and divide the field into quarters coverage (each taking 1/4th the field) or three might play a quarter, quarter, half scheme. Cover 2 as an alignment shell is popular simply because it can convert to many other actual defenses after the snap of the ball and lends itself to confusion. (Come on - you didn't really think that USC was playing the same defense on every snap did you?)
Here is an example of what the quarterback sees when he lines up and the defense is in a Cover 2 shell with a 4-3 Over alignment up front. The trademark look of this defense is having two safeties high or back deep. Unfortunately with the narrow TV viewing angle you don't often get a nice view of this from home.
Here is a sample picture when you could see on TV that USC was playing Cover 2 right before the snap off the football.
Unfortunately even with this wide of a viewing angle you can't see the remaining deep safety who is just out of the TV picture...
Cover two simply divides the field into zones for the five underneath players (2 corners and three linebackers) and two deep zones for the safeties to play. As you can see by the diagram the underneath passing areas for short curls, slants, dig routes, screens or quick out patterns are quite crowded. Pass plays into these areas normally at best gain only a couple of yards unless the defense misses an assignment. Errant throws by the quarterback under pressure have a strong change of being picked off. Pressure via the front four defenders is critical for Cover 2 to work as there are no additional blitzers coming from this base defense.
Just like any defense however, Cover 2 is not without its soft spots. It is vulnerable to giving up small chucks of yardage on a consistent basis if well executed by the offense. USC had some difficulties last season when teams with veteran QB's went into spread offensive sets and consistently made first downs. Washington and Washington State both played virtually mistake free on offense with no turnovers against USC in 2006. Both teams moved the ball at times and more importantly did not give the ball back to the USC offense. Out of the Shotgun formation the QB's were able to read the defense and pick open the small underneath areas between defenders with some degree of success. Here is an example from the Washington game of a spread formation that was frequently used with 3 WR's a Tight End, and a Running Back. I don't recall for sure but it appeared that on this play USC played two safeties deep in zone coverage since it was 2nd and 10 and played man coverage underneath. Spread formations such as this one force the defense to decide on second down whether to stay with base personnel and split out a linebacker on a receiver in the slot or put a 5th defensive back in and remove a linebacker.
If the defense can not apply pressure and the quarterback has about 3 or more seconds to throw the ball then some other soft spots occur in the Cover 2 secondary. Here is a stereotypical example of where those soft spots occur.
With a clear 3 seconds to throw the ball without pressure the WR's will find designated areas of the cover two defense. Every defense has soft spots and offensive coordinators are skilled at attacking them. USC for example has a whole list of plays kept in reserve each game called "Cover 2 Beaters". So does every team for that matter and for every type of coverage. Those plays are specifically designed sets to put receivers into the soft spots where defenders have a hard time reacting to the ball before it arrives. Every offensive coordinator knows these soft spots even if fans don't realize it...The problems is having quarterbacks that can read the coverage, an offensive line that can provide enough time to make the pass, and WR's skilled enough at route running to get past corners that often bump or jam them on the line of scrimmage and still exactly get into the right position at the split second the ball arrives. Remember .1 second is about all that separates a completed pass from and incompletion or interception.
What type of plays work to get into the soft spots of Cover 2? Tight ends releasing into the middle of the field on a seam route up the middle works. In reaction to this some teams drop the middle linebacker with the tight end into the middle of the field. When this tactic is employed technically it is a Tampa 2 defense that is a four underneath zone with three deep and the third deep person is a middle linebacker that can run with the tight end.
Another pass play is an out route or anything that puts the WR into the area past the corner backs (who stay in underneath zone) and in front of the safeties. The quarterback throws the ball towards the outside shoulder of the receiver so that only he can make a play on the ball. Mitch Mustain the heralded incoming QB from Arkansas completed one of these against USC's cover two late in the 4th quarter in his first series on the field in game one of the 2006 season. He then also on the next drive threw an interception right into an underneath zone covered by retreating LB Thomas Williams on the next series...
To really attack cover two however coordinators often employ pass routes in combination such as double slants, double posts, and combinations of hitch routes and deeper routes. The idea is to put multiple receivers into a zone area and make it impossible to cover both. The safety eventually has to commit and then the quarterback reads this (assuming there is time to make the throw) and throws to the other receiver in the area.
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It all sounds simple on paper but in reality a million tiny executional details happen on every pass play. The defensive coverage might stem into something unanticipated (e.g. go against tendency) after the snap. Pass protection might break down in 2.5 seconds or less forcing a play to a check down receiver, WR's might get jammed at the line and have the route timing thrown off, or the QB might read the play wrong or make a poor throw.
If you want to learn more about attacking cover two or any defense that uses two high safeties then I suggest ordering a copy of Attacking Two High Safeties a 55 minute DVD by Gunter Brewer WR Coach and Passing Game for Oklahoma State.