USC Interceptions 2003-2005 I ran across a comment in a coaching presentation that was apparently made by Tony Dungy. I couldn't find the direct quote by Dungy but the relayed version was something to the effect that the vast majority of interceptions in football are made by defenses playing in zone coverage (Cover 2, Cover 3, Cover 4, etc.). However zone based schemes also tend to surrender a slightly higher pass completion percentage. In contrast man defense schemes allow a lower pass completion percentage but tend to give up the dreaded bigger play especially if there is no one defending the deep middle third as a safety.  So of course all teams mix and match their coverages. That was the gist of the comment as I recalled it. Unfortunately the narrow TV viewing angle at home is just not designed for this sort of observation and the announcers on TV are of little help. Teams routinely align in a two deep coverage shell and then rotate into something else after the snap when fans can't see. Here is a link to a few plays from the start of the Indianapolis versus Bears Super Bowl game a year ago with the coaches film using both end zone and sidle line views. The general sports media often seems to think that the Colts solely play 2 deep coverage or the two and a half deep Tampa 2 style of coverage with the MLB dropping intermediate to deep middle. However if you watch the secondary closely you'll see what I mean about the mixing and matching. Pretty clearly one deep safety and man under coverage is played on several of these plays and some two deep coverage alignments rotate to one deep man under coverage, etc. There is a near interception by the Colts free safety on a deep ball. If we watched enough of the game the Cover 2 and Tampa 2 schemes would eventually show up for the Colts as well but not as often as you might suspect from listening to the general media. Link to 2 minute Colts video clip On the Bears defensive side versus the Colts offense it is more of the same. These clips show an even more pronounced use of aligning in 2 deep safety schedules and then rotating one safety down hard after the snap to make it a one deep coverage scheme on the first two plays. On the following plays there is some bluffing and eventual playing of two deep or perhaps Tampa Two in one case. There is also a Peyton Manning interception versus 2 deep zone coverage combined with what appears to be man coverage underneath. The safety makes the interception effectively reading the QB on the pass play as Dungy predicts in general. Perhaps Manning even expected the Bears to rotate to a one deep scheme where the safety would not be able to arrive in time? Link to 2 minute Bears video clip This is too small a sample size of course to make any strong points based upon the video. And of course the real world has a lot more variations and "in-between" cases such as zone blitz schemes where the defense overloads one side of the line and puts pressure on the QB. Behind this they might play either man or zone depending upon the exact nature of the blitz, the formation, and WR patterns anticipated by the defense. Still however this notion made a lot of sense to me that interceptions are in general more likely to occur in zone schemes where the defensive backs and linebackers are able to watch the play develop in front of them and watch the quarterbacks footwork, eyes, and shoulders more thoroughly. In man coverage with their back to the QB there are fewer good chances for interceptions. Hence good teams mix and match their coverages accordingly  on down and distance and try to fool the opposing QB by aligning in one scheme and then playing another post snap, etc. In USC's case this is certainly true as least as explained by their secondary Coach Rocky Seto in a short summary I posted a month ago. After the presentation however I wanted to go back and look at USC's interception trend again and look at a couple things more closely. As noted many times on this site turnovers forced by the defense are down the past two seasons at USC especially in terms of interceptions. Here is the trend for just interceptions broken down by position for the past several years. As you can see below both interceptions by the secondary and linebackers are off their normal marks. I put some data into a spread sheet using Google Docs and you can access it here if you are interested (click). Just please don't accidentally delete it as it may be configured for open access. I have not used this much yet but it looks promising for sharing data. Copy the contents and put into another spreadsheet if curious. I meant to take the data as far as 2007 but I ran into some other work and never looped back to finish it up. Also ideally there should be a few more columns that indicate what defensive front the Trojans played, what secondary scheme was played and what if any type of stunt, dog, or blitz was executed. I never got around to that eand the TV angle does not really allow for that detailed of a look. Still I will show the TV video below for anyone interested. First however the basci game data from 2003 to 2005. First in terms of down and distance two things jump out when you sum and chart the data. Number one interceptions happened fairly equally on every down whether it be first, second, or third. I had initially expected to see more on third down but that was not the case at all. Second and perhaps more predictably in all cases interceptions came in passing situations of 10 yards to go (or more). 43 of the 66 interceptions in the three year period came with 10 yards or more to go (i.e. obvious passing situation). In terms of when the interception occurred it was fairly balanced as well by quarter with an upswing in the 3rd and 4th quarters when teams are behind and more likely to be throwing. However there were still 28 interceptions made in the first two quarters versus 38 in the latter two. If you mix in fumbles as well the probability of a turnover is virtually equal in each quarter regardless of score. For those curious in the actual interceptions 66 is a lot to put into one video clip so I edited it down to just the 22 recorded in 2004. I organized the interceptions by position (linebacker, secondary, and defensive line) and will put it here for those interested. As you can see the linebackers did a tremendous job that season of making big plays on defense and dropping back in the passing game especially LB's Tatupu and Grootegoed. The front four did a nice job as well applying pressure. However only on two of the clips did I see an extra Trojan defender rush in addition to the front four putting pressure on the passer. One was a zone blitz where Lawrence Jackson dropped into coverage. Blitzing as Dungy noted probably forces quicker throws and leads to a lower completion percentage. Interceptions are more likely in zone coverage. Coaches thus wind up mixing and matching coverage schemes and alternating types of pressure. Unlike the Super Bowl clips I don't have the side line and end zone views of the USC defense so the following video clip is not ideal for identifying some of the details. You should see some good examples of zone coverage and some with one or two deep zones combined with man underneath coverage on different plays. I was also unable to account for changes in personnel on the field (e.g. regular versus nickel, etc. as well) due to the viewing angle and TV coverage. Link to 12 minute USC interception video clip This is as far as I pushed the study before running out of time. If and when time allows I'll attempt to expand the look to 2006 and 2007 as well to see what if anything jumped out in terms of difference. I suspect there were simply a lot of near misses in the interception department the past two years and a split second hear or there would make a lot of difference in terms of results. Still in 2008 the back seven could be the most talented of the Pete Carroll era. I'd like to see interceptions get back to the level of almost two per game or 20+ per season as in previous years. That will be an interesting subplot in 2008 and a big help to the offense if it occurs as well.