The Value of a Cornerback
After writing yesterday about Cameron Wake and trying to put a value on the pass rush I wanted to take a look at the corners in a similar manner since our own Darrelle Revis seems to be looking at a getting a deal that is closer to that of DeMarcus Ware than that of Nnamdi Asomugha. Now I had done something a few weeks back on ranking the corners in terms of plays made, but this time around I want to look at corners in terms of raw success and failure. And again a big shout out to Pro Football Focus for compiling the raw data so I can fool around with the numbers.
While the CB at times is called on to cover tight ends and runners, for the most part their job is to cover wide receivers. So to define success rates I wanted to look at WR’s in 2011. The average WR was targeted 19% of the time he went out on a pass pattern, of which he caught 59.2% of the passes and failed at making a catch 40.8% of the time. So right there we have our three numbers we really need to determine the value of a corner just in terms of success and failure. On a per snap basis the player normally will have success on 11.24% of the snaps and failure on 7.75% of the snaps.
To illustrate the scoring metric, I will use Revis as an example since he is pretty much universally recognized as the best in the game. Our first step is to calculate the number of times a player is thrown at based on coverage snaps. Revis was thrown at 85 times on 553 snaps, which means 15.37% of the time in coverage. Now we want to know the percentage of receptions that are credited as being against the corner. Revis allowed 41.2% of his targets to be caught, which means the opposition was unsuccessful 58.8% of the time. Multiplying those figures we can now say that we can say that his assignment succeeds 6.33% of the snaps. If the receiver was expected to be targeted 19% of the time it means Revis’ assignment failed 12.67% of the time. So now we can say that Revis increases the chance of receiver failure, defined as a completion or incompletion, by 63.4%. That’s pretty impressive but it’s actually not the best in the NFL. Actually he only ranks 5th.
Surprised? I was as well. Revis clearly is the most active player and knocks down more passes than anyone else in the league. But the reason he doesn’t rank first is because of prevented attempts. The effect of not being thrown on is something I had not considered in my previous run through corners. It’s a total failure and a complete shutdown. Here is the top 10 as a percentage of snaps, with the final category showing how much more effective the player is at causing an incomplete pass.
This changes the results dramatically of the top 10 I had done before. Asomugha, who still is rarely targeted despite not being very effective when thrown on, and Robinson, who is ok in coverage but gives up huge yards when he fails, showed huge gains. The others all ranked top 10 except Brown and McCain, who didn’t qualify for the 3 year survey, and Marshall. Jacob Lacey is still the worst.
However, after doing this I realized that maybe I am valuing the prevented attempt too highly. This chart is representative of receiver failure but not play failure. The coverage failure is a failed play. It’s incomplete or turned over. There is no second chance. A prevented attempt simply funnels the pass from WR A to WR B. 40.8% of the time it will fail, so really the prevented attempt is only causing 0.408 failures, not a full failure like the coverage breakup. This would be the new top 10 ranked in terms of causing a full play failure:
Maybe this doesn’t factor Revis entirely correctly since he does often, but not all the time, match up with a 1 while others split time, but this chart correlates much better with the actual activity numbers from the prior analysis with Sheldon Brown being the big mover. Without per snap coverage assignments known for every play it would be impossible to calculate accurately. The major difference would be targets as the average of the top 20 targeted receivers is 23.7% of the time compared to 19% for the entire pool. Completion percentage is still right around 60% for that group. If we had that data we could run it for every player to get a far more accurate assessment but right now this is the best we have. Asomugha drops like a brick because his actual success when thrown on is so poor, allowing over 61% of his targets to be completed.
For whatever reason Revis does not get the same respect in coverage others get. Maybe it’s the scheme and he is far more man on than others. Maybe it’s the grading system used. Maybe its just that many more grade A assignments, Asomugha only gets picked on 8.7% of the time he is on the field while Revis is over 15%. I think that’s far too much respect given to Asomugha, but that’s how teams are approaching his zones on the field.
I think there is still a way to utilize both charts. If you happen to play in a pass happy division, where you have 6 games guaranteed against teams flinging the football, the actual play failure chart is more valuable. You would rather have players causing a failure then allowing the play to go to someone else. I think that’s the trap the Raiders fell into when they gave Asomugha all that money. Plays just went elsewhere and were successful. If you take someone from the first list in that scenario you are best suited to pair him up with another big time player. This is what the Jets have done with Revis and Cromartie and what the Eagles did last season. The Jets is probably overkill since both Revis and Cromartie do stand out individually, but both are really wrecking games.
Now if you play in the division that doesn’t throw the ball, has bad QB play or only 1 passable receiver per team, say the NFC West or AFC South, maybe it pays to go for broke and bring in a guy like Asomugha. The fact that teams don’t throw at him might really hurt them. Revis, Taylor, Grimes, etc… all fit against any competition. But you cant even think of building a defense around someone like Asomugha. Maybe he needs to do more like Revis and at times try to bait someone into throwing the ball and then making a play on it.
For the other Jets players Cromartie ranked 5th out of 66 players and a failure rate of 26.05%. Based on the first criteria he was number 12. That’s pretty excellent. He was near the bottom of the NFL in plays that went for scores, though so his receptions do come at the worst time. Kyle Wilson ranked 58th and 59th in the two charts with negative failure rates of 3.2% and 16.6. That’s pretty terrible. Drew Coleman, who the Jets are showing interest in, was 63rd and 64th. He was a -22.5% and -27.4%, which is brutal. I can’t see any reason why the Jets would revisit that.
Going back to the topic of the pass rusher vs corner I think it’s tough to say that a corner should be paid anywhere near them. Using similar criteria we came up with a play that hurries the QB to lead to a 59.2% increase in failure. Revis caused less than 36%. Now corners are involved in more chances, but Revis’ play failure number of 10.7% last season would be a little lower than the same failures expected by Tamba Hali. Hali earned a contract paying $11.5 million a season, the same number as Revis’ current deal. This also wouldn’t even take into accounts that pass rushers who play both ways, like a Ware, contribute to the run defense. Revis, who is very good in run support, only has 1.7% of his run support be considered a negative play. DeMarcus Ware had 8%.
I think it’s tough to justify a significant raise for any corner. It is hard to come up with a reasonable way to say they are going to effect a season that much more than a DE or OLB. Now that doesn’t mean I would say that money invested in a pass rusher over a corner in free agency is money well spent. One thing that surprised me in going over the OLB numbers was that most of the good players are on rookie deals. Ware is the exception, but nobody else including the superstars like Julius Peppers, was exactly justifying the big money spend. Look at how much Calvin Pace has been a bust as a pass rusher. The corner list is loaded with veterans rather than rookies. In the future it might be something worth looking into if the pass rusher market is somewhat overvalued when the players hit free agency. Its probably better to develop from within, extend early, and then cut bait before you get stuck with megamoney on the end of the deal with limited results. The Jets seem to be trying to do just that by drafting Quinton Coples and carefully evaluating Aaron Maybin rather than going wild in free agency. Its the one way to keep their corner tandem intact and still have a chance to improve up front, provided of course that Revis doesnt end up with a new deal paying him $15 million a season.