Ranking the NFL Cornerbacks
This is really an expansion on some work I had previously done looking at cornerbacks and ways to determine an actual ranking for the corners under a few different criteria. In my prior model I focused on basic receptions for the 2011 NFL season. Here I wanted to expand this to now include 3 years of stats, weighted in a 50-35-15 proportion, and adjust the stats a bit further than before.
First we need to examine the standard WR performance for a player who participates in 50% or more of the snaps for his team in a number of categories that include pass routes, snap counts, slot targets, slot receptions, slot yards, outside (non-slot) receptions, outside targets, and outside yards. Though a corner doesn’t cover a WR exclusively that is their main assignment for a majority of the game. Averaging out three years of data we have this as the expected performance for a starting NFL Wide Receiver.
The numbers are relatively consistent despite the changing faces in the mix each year. We can use the average numbers and apply them to each cornerbacks performance to make estimates of how many yards the player should have given up, how many receptions he should have given up, and how often he should have been targeted based on the number of coverage snaps the player had. This will allow us to extrapolate two rankings- one of which is a shutdown ranking and the other which measures the overall effectiveness of the corner if paired with an average player. The corners we will be looking at are those who have played at least 50% of the snaps the last three seasons in the NFL, basically meaning they are the top line starters in the league. Only 32 players qualified.
The Shutdown Stat
Our first numbers in the chart at the bottom of the page are what I call the shutdown categories. This is quite simply how much a corner is dominating his one target in the game. It reveals how many receptions above or below the norm is expected of the cornerback. The shutdown only takes into account 1 target on the field. This can be done by pass prevention or target prevention. For instance assume the average WR lines up against Nnamdi Asomugha of the Philadelphia Eagles. Asomugha lined up in coverage 540 times in 2011 and we know that the normal target per route run is 20.2%. We can now say that Asomugha should have been targeted 108.8 times in 2011. Using his personal mix of slot vs outside coverage we can further say 27.7 of those targets should have been in slot coverage and 81.1 in outside coverage. Knowing the normal catch rate in both the slot and outside the expectation is 18 and 47.5 receptions respectively for a grand total of 65.5 receptions on the season. Knowing the YPC in each category we can also determine that he should have allowed 967.8 yards on the year.
Asomugha’s actual performance is 29 receptions for just 376 yards. Clearly that is the sign of a shutdown cornerback. We now rate his shutdown scores at -55.8% and -44.3%, which rank one and five respectively among our corner sample. This number tells us that Aso’s receivers are catching about 55% less passes than expected for 44% less yards than they would normally get in a game. That’s pretty dominant and why he commands so much money. The average score among the group is -26.4% and -15.43%, so Asomugha is pretty good in that regard. For that matter so is this entire group which is why they, on average, are holding wideouts to below their usual norms. There are only 7 players giving p more yards than expected and none giving up more receptions.
Asomugha shuts players down by simply being a blanket in coverage or being respected as a player you don’t throw on. His actual performance when thrown on was just average. That of course brings up the question about what happens when an Asomugha simply prevents a target rather than preventing a catch? The answer exposes one of the fallacies about valuing the shutdown corner as so important to the success of a team. There are 10 other players on a team, two of whom are likely in coverage against wide receivers, and two of whom that are trying to lock down a tight end or a running back. All Asomugha is doing is filtering the target from option A to B. So we need to adjust for that since paying Asomugha $12 million a season does no good if he is playing alongside an average or worse NFL.
To make that adjustment we will make the assumption that the QB is choosing to throw to another wide receiver on the field. Since slot throws are often first reads we will assume that all coverage options lead to a throw to an outside wide receiver. From the table above we know that the outside receiver is going to catch the ball about 58.6% of the time. So going back to Asomugha, his real performance would be to see the opposition end up with 65 receptions for 891 yards on the season. That’s still better than expected, but by no means is it a dominant performance. In fact it’s pretty close to the expectation if he was just an average player.
This is the reason why Asomugha was such a failure on the Raiders. It does no good to have a grade A cover corner with average and below average players elsewhere on the field. It just leads to the 2 and 3 targets putting up the good fantasy game of the season while the owners of the grade A get upset that their player had a bad week. This is why the weaknesses on the Jets at cover safety and linebacker was so glaring to the fanbase. Teams avoid Darrelle Revis and Antonio Cromartie, not to the extent of Asomugha, which leads to big plays for those alternative weapons on the field.
Revis, the Greatest?
Because Revis does get thrown on and he seems to bait people into throwing at him he will never garner a shutdown rating as high as some others. His worst of the three seasons I judged was actually 2009 in this regard, which was caused primarily by the fact that teams showed him no respect and constantly threw at him. His ranking from 2009 is 20th in shutdown receptions and 7th in shutdown yards, meaning people threw very short completions on him, out of the 96 seasons surveyed. His 2010 season ranked second to Asomugha in 2010 for shutdown receptions and was Revis’ best showing in that category.
Revis’ real value comes from those bait tactics. He isn’t letting the ball cycle elsewhere and the Jets are far better off seeing the ball come flying at him and his catch rate in the 40%’s than at a Lito Shepppard or Drew Coleman type. His 2009 season was just unheard of and something neither he nor anyone else will approach again. His 2009 reception reduction was -37.5%. The next closest player was Ike Taylor in 2011 at -25.4%. His yard reduction was a whopping -57.2%. Taylor was next at -40% in 2011. That year resulted in teams failing to complete a throw 53.8% more times than usual against him. Taylor’s 2011 was the next closest at 37.6%. Those numbers are just obscene for Revis and so far off the charts that nobody will likely ever approach them again.
All three of Revis’ seasons rank in the top 5 of the last three years in receptions and in failed plays. So he is clearly consistent at a position where there are some big swings in performance. But Revis has fallen in the key category of yards. While he produced the best ever season in 2009, 2010 ranked 37th among the 96 seasons. 2011 was 14th. These numbers are much closer to the mean of the group which is to hold players to about 14% below the expectation. That doesn’t make them bad by any means and they were both above average, but teams are having some success against him by heaving it further.
Whether or not Revis is the greatest depends on the ranking criteria. Using the weighted system which puts more focus on 2011 than 2009 he no longer ranks tops in yards. If we look at overall receptions he is clearly the best. His -25% score is 8 points higher than the number two player- Antonio Cromartie, also of the Jets. The average score among the group was only -3.3% so Revis is so far ahead of the field due to consistency and general awesome play.
Yardage-wise he has slipped, though not terribly. Brent Grimes of the Atlanta Falcons ranked number 1 with a -31.7% while Asante Samuel, now with the Falcons, was second with a -28.9%. Revis was third with a -28.7%. Taylor was 4th while Cromartie was fifth in the category. The top 4 stand out as a rather elite grouping with Cromartie not too far behind.
Looking closer at the seasons it’s at least arguable as to whether or not he is the best in the game, which was not even a question two years ago. Part of Revis’ weighted ranking is still heavily dependent on that 2009 season. 2010 was a down year as he battled injuries that were likely caused by his decision to hold out through training camp. Revis ranked second in overall receptions (behind Cromartie) but ranked 12th in overall yardage behind a huge list of players. Cromartie was actually the more effective player in 2010. 2011 was a bounce back but again he failed to be first in either category. He was again second in receptions, this time to Ike Taylor, and 5th in yards behind Taylor, Grimes, Samuel, and Cortland Finnegan.
When you factor in the ability to be a shutdown player and the fact that he can be a drive killer by preventing receptions I’d imagine it’s pretty clear that Revis is the most consistent player in the league at the position. The gap isn’t as big as it was in 2009 and if you don’t mind giving up small plays there are probably cheaper options out there, but Revis is the only guy who you know really gives you everything. But he is going to have to keep playing at an ultra high level if he is to earn the money that he wants from the Jets. If he continues to play at the 2010 and 2011 level there will be a number of players, such as Grimes, looking for some big dollars next year and having the stats to back it up.
The stats kind of debunk the argument that I have made many times about cornerback investments. Is Cromartie and Revis overkill? Maybe, but if you are going to invest heavily in Revis it does no good to have your number 2 be Kyle Wilson. That is where you end up with the Asomugha on the Raiders situation. Maybe they don’t need an elite corner to pair with Revis, and Cromartie has been close to elite, but he has to be above average. If you don’t pair him with that type of player you may as well just let Revis walk. I’d imagine this is the very reason why the Eagles have gone big into corner talent, as have the Falcons. You cant just overpay for one…you need two.
That said you still have to make a choice at that point to either fill the team with pass rush potential or spend a bit less on CB2 so you can beef up the safety positions. Teams like the Jets match up poorly with the Patriots because New England presents weapons that totally neutralize having two quality corners. You can only beat that with better secondary talent or with players that cause failures through the pass rush. What you cant do is waste a first round pick on a third corner as the Jets did in 2010.
On the salary front, since that always comes up with Revis, it is tough to make the argument that this is as valuable as a pass rush. In our look at pass rushers there is a clear effect that the rush has in the efficacy of the secondary. I don’t have stats to describe the effect the coverage has on the rush, but from watching the games how often do you see coverage sacks or pressures? I don’t think too often and certainly not as much as the other way around. Your pass rushers also mainly play all downs while corners are somewhat worthless on run plays. Corners also have pass plays in which they will never be tested simply by play design. To me that is less of a concern for the pass rusher who is pretty much active on every play.
With more data we can further adjust these scores for a few other scenarios. One that I would like to do is deep passing. Passes that travel more than 20 yards have a significantly less chance of being caught than those under 20. I think it would be valuable to look at results as under 20 slot throws, under 20 outside throws, and over 20 throws to see just how much corners benefit or are hurt from the pass selection.
Secondly I think the stats should be adjusted for pressures and sacks. Asomughas coverage has little to do with preventing a target when Jason Babin sacks the QB. I’d imagine a player like Ike Taylor has benefitted from a defense that pressures the QB more than others. It also was probably a factor in why Revis’ 2009 season was so incredible since the Jets took the world by storm with their blitz schemes that season. Remember that was the year the Jets didn’t get exposed for Sheppard and friends until they matched up with Peyton Manning. Those stats are somewhat available but would require a great deal of time to look at for each team by season.
Finally it would be nice to get breakdowns of coverage by position. This study makes the assumption that a corner only covers a wide receiver. While that is often the case they do have other assignments on the field. Those assignments can skew the overall data. To adjust we would need to know how many coverages a player has against a certain position each season and as far as I know nobody tracks that, at least in an easily usable format.
An Offseason Wrapup
Well this is probably it for the offseason writing topics unless I finish up a cap study I was working on. From here on out well mainly be looking at the Jets season unless an important topic pops up or someone emails a request for a specific valuation/analysis. Thanks for keeping the site alive this offseason by reading some of the things I threw out there and suggesting items to write about. And the contract tips are always appreciated even if it’s something you think I may have already seen.
Special thanks to Pro Football Focus for publishing so many stats that I can work with for my contract and positional evaluations. I’d also like to thank David Fisch for helping edit and correct so many grammatical errors that I make (and will continue to make). David volunteered his time for me before his school commitments took precedence and it was really appreciated. And of course all the folks over at The Jets Blog for driving some traffic my way with the salary cap updates and links to certain items I write.
Lets hope for an improved season for the Jets as they make their way back to the playoffs rather than the implosion we witnessed last season. They have a strong defense in place and if the QB position sorts itself out I think they have a good chance to be back in the playoffs this year.
Cornerback Rankings, 3 Year Weighted Average
|Name||Shutdown Rec.||Shutdown Yards||Overall Rec.||Overall Yards||Increased Failures|
- Bent, TJB
However, there's something to be said about coverage scheme and quality of safety play as well. We all know that Revis very rarely gets over the top help compared to Cromartie, or many of the other guys, so he's got to protect against the deep ball moreso than most others (which he does phenomenally). Obviously with Pittsburgh's situation, Ike Taylor has Troy Polamoulu playing centerfield preventing a lot of completions.
Also, Aso's "amazing" '09 was partly due to the fact that he wasn't covering the best WR on the field, the Raiders actually doubled the best WR on one side of the field and Aso covered #2 one-on-one. Shutting down a #2 isn't nearly as impressive as Revis shutting down the likes of Reggie Wayne, Randy Moss, Calvin & Andre Johnson, etc.
Just proves that there's so much that goes into football its hard to quantify perfectly a specific position. You do a great job though Jason, and I really appreciate what goes into these studies and I enjoy reading them.