Writers of Pro Football Prospectus 2008

Most Recent FO Features


» A History of Undrafted NFL Quarterbacks

Given the historical success of undrafted quarterbacks in the NFL, Tony Romo might as well be a national treasure. We look at the impact of developmental leagues on undrafted quarterbacks, and just how many players have tried to break through in a recent season.

04 Feb 2010

Stat of the Day: 2009 CB Charting Stats II

by Aaron Schatz

As part of our ongoing Stat of the Day series, we've spent the past four weeks digging deep into our spreadsheets to run a new stat every weekday until Super Bowl XLIV (well, until today... this is going to be the last one, so that the Super Bowl preview can get everybody's full attention tomorrow).

Yesterday we took a look at the best cornerbacks of the season according to the FO game charting project. Today, we'll flip things around and look at the corners who rank at the bottom of the game charting stats. I've ranked all cornerbacks with at least 40 charted passes, which means 70 total cornerbacks. I've removed passes marked as Hail Mary, Hit in Motion, Tipped at Line, or Thrown Away. I've also removed wide receiver screens, which aren't really a good way to measure cornerback coverage because a cornerback in man coverage is going to (or at least, is supposed to) immediately get blocked out of the play by another wide receiver. Right now I'm only looking at primary defenders, so this is not adjusted to account for double coverage, or plays where the charter marks a hole in zone but lists an appropriate zone defender in the second DEFENDER column. There are no opponent adjustments yet, and pass interference is not yet included.

Typical caveats apply, of course: This is imperfect data based on the game charting project, which means it comes off limited television camera angles. In past years, this data has been very inconsistent from year to year, and we're going to study that in the offseason to try to figure out if we can get more accurate numbers by, say, looking at players over two-year spans.

Success Rate, to remind everyone, is the percentage of passes that don't manage to get at least 45 percent of needed yards on first down, 60 percent of needed yards on second down, or 100 percent of needed yards on third down.

Bottom 10 Cornerbacks in Success Rate, 2009 (data as of 2/3/10)
Player Team Charted
Yd/Pass Rk Avg. Pass
YAC Rk Success
20-N.Harper TEN 63 8.8 61 9.4 3.2 24 38% 70
23-M.Trufant SEA 55 9.6 65 13.0 4.9 62 40% 69
23-T.Jennings IND 65 6.4 18 10.1 1.8 4 42% 68
21-V.Davis MIA 47 12.6 70 12.7 6.0 67 43% 67
24-R.Bartell STL 61 9.5 64 12.5 4.7 56 43% 66
31-F.Washington BAL 42 11.6 69 11.9 6.4 69 43% 65
23-C.Houston ATL 51 8.4 58 14.0 1.8 3 43% 64
26-K.Hayden IND 48 8.1 54 11.9 2.9 20 44% 63
27-M.Jenkins NO 41 10.0 67 11.2 6.4 68 44% 62
35-Z.Bowman CHI 54 8.2 55 13.1 2.8 16 44% 61

At what point have we compiled enough data showing that Marcus Trufant came back from a back injury far below 100 percent health? Not only is he near the bottom in the charting stats, he also managed to get penalized for defensive pass interference seven times in just ten games.

You may notice some players on this list who will be appearing in the Super Bowl this Sunday. Tim Jennings is here because of the Colts' defensive philosophy: prevent the big play, even if it means allowing a first down. Malcolm Jenkins is here because he was god awful as a rookie. Kelvin Hayden is probably some mix of the two -- he's been better than this in previous years, and I'm a little surprised to see his stats so low. (Maybe this is just a product of the year-to-year inconsistency of the charting stats; as I say above, we're going to study it in the offseason.)

Bottom 10 Cornerbacks in Yards per Pass, 2009 (data as of 2/3/10)
Player Team Charted
Yd/Pass Rk Avg. Pass
YAC Rk Success
21-V.Davis MIA 47 12.6 70 12.7 6.0 67 43% 67
31-F.Washington BAL 42 11.6 69 11.9 6.4 69 43% 65
24-S.Smith MIA 49 10.1 68 15.8 4.3 50 59% 11
27-M.Jenkins NO 41 10.0 67 11.2 6.4 68 44% 62
22-B.McDonald CLE 56 9.7 66 13.3 7.0 70 57% 19
23-M.Trufant SEA 55 9.6 65 13.0 4.9 62 40% 69
24-R.Bartell STL 61 9.5 64 12.5 4.7 56 43% 66
24-J.Wilhite NE 53 9.4 63 13.8 3.8 42 49% 51
21-D.Cox JAC 86 9.2 62 12.9 2.9 18 47% 55
20-N.Harper TEN 63 8.8 61 9.4 3.2 24 38% 70

This mix is a pretty good mix of the old (Nick Harper), the slowed by injury (Trufant), and a lot of rookies and near-rookies (pretty much everyone else). The exceptions are Ronald Bartell, who's never had good numbers and isn't exactly getting help from a good pass rush in St. Louis, and Fabian Washington, whose really poor charting numbers are a bit of a mystery to me. I've always thought of him as average, not terrible.

The numbers for Brandon McDonald and Sean Smith are particularly interesting, since they end up as mirror-universe counterparts to the Colts cornerbacks. You might remember McDonald from his adventures getting completely toasted by the Denver Broncos on an NFL Network broadcast, Thanksgiving evening in 2008. His numbers from 2009 show he did a much better job of coverage overall, but he's still toaster-friendly. When you beat Brandon McDonald, you really beat Brandon McDonald. He is listed as DEFENDER1 on five passes of 40 or more yards, including a 72-yard Derrick Mason touchdown. (The charter did mark that one as double coverage, with Abram Elam as the deep safety help who also got beat.) Miami rookie Smith had an even better Success Rate than McDonald, but gave up three passes over 40 yards and another three between 30 and 40 yards.

Bottom 10 Cornerbacks in YAC Allowed, 2009 (data as of 2/3/10)
Player Team Charted
Yd/Pass Rk Avg. Pass
YAC Rk Success
22-B.McDonald CLE 56 9.7 66 13.3 7.0 70 57% 19
31-F.Washington BAL 42 11.6 69 11.9 6.4 69 43% 65
27-M.Jenkins NO 41 10.0 67 11.2 6.4 68 44% 62
21-V.Davis MIA 47 12.6 70 12.7 6.0 67 43% 67
22-A.Samuel PHI 53 8.1 53 10.5 5.6 66 55% 29
23-C.Griffin MIN 51 8.1 52 10.6 5.5 65 53% 38
20-C.Gamble CAR 49 8.4 57 9.3 5.0 64 45% 58
24-S.Brown PHI 72 7.2 36 12.0 4.9 63 63% 6
23-M.Trufant SEA 55 9.6 65 13.0 4.9 62 40% 69
22-T.Porter NO 68 6.3 15 11.7 4.9 61 54% 33

Can someone please teach the Philadelphia cornerbacks to tackle better? Thanks.

Posted by: Aaron Schatz on 04 Feb 2010

17 comments, Last at 07 Feb 2010, 2:51pm by Vince Verhei


by alexbond :: Thu, 02/04/2010 - 4:27pm

So what are Trufant's chances of returning to Pro Bowl form next year?

by frankieg33 :: Thu, 02/04/2010 - 4:54pm

What are the reasons Bowman is on this list? Trying to ball hawk it too much or Tillman?

by Charles Jake (not verified) :: Thu, 02/04/2010 - 6:02pm

The main reason is probably that the Bears' defensive philosophy is similar to the Colts': allow the catch, avoid the big play. The Bears' tackling has generally been poor, too. Bowman did lead the Bears in picks, so there's probably some ball-hawking involved.

by Chip :: Fri, 02/05/2010 - 12:21am

Very true. His YAC allowed is 16th, which supports your point. He's clearly not as good as Tillman. He had a decent first year as a starter, but was absolutely torched by Megatron when he faced him.

by Duke :: Fri, 02/05/2010 - 12:17pm

I charted quite a few Bears games this season and this basically mirrors my impression, too. The Bears also played their corners far off the receivers (not sure if this is the same as the Colts), which led to a lot of catches further down the field.

by bravehoptoad :: Thu, 02/04/2010 - 8:04pm

I'm surprised how bad Vontae Davis is. I hadn't heard him play -- only seem him on the occasional highlight reels, and I thought he was doing pretty well. But yipes. No. Worst yards per pass of anyone.

by Danish Denver-Fan :: Fri, 02/05/2010 - 8:08am

Agree. I actually saw a couple of Dolphins games, and I was actually impressed. Hmm, I'd be interested to hear from some Dolphins fans. The charter perhaps?

by fyo :: Fri, 02/05/2010 - 6:59pm

I've seen every phins game this year and came away impressed with Vontae. Sean Smith started off impressing me, but didn't seem to improve much over the year.

I'm SHOCKED that Vontae is this low on the charts and I have to say, I wish the results were accompanied by an indication of the variance in the underlying data. The success rate does give a hint, of course, but I suspect the numbers of several of the low scorers are skewed by a few huge gains on long to-go distances, coupled with a bunch of 4 yard receptions with 3 to go.

The "slope" of the player performance according to success rate is also quite flat for the most part. If you look back at Part I, exactly 2 cornerbacks scored in 70s, 8 in the 60s. So once you get to #10, you're already looking at success rates in the 50s.

The drop from #1 to #9 is 12 percentage points.

The drop #10 to #67 (Vontae) is 16 percentage points.

I.e. HUGE drop off initially, followed by a very long tail where the players performance was actually quite close.

by fyo :: Fri, 02/05/2010 - 7:26pm

Replying to myself here...

Having already established how close the field of CBs is once you get out of the very top, it becomes increasingly important to look at performance parameters not covered by the stats. E.g. interceptions.

Nick Harper 1
Marcus Trufant 2
Tim Jennings 2
Vontae Davis 4
Ronald Bartell 0
Fabian Washington 0
Chris Houston 1
Kelvin Hayden 1
Malcolm Jenkins 1
Zack Bowman 6

Pretty big difference. If you were to calculate some sort of DVOA, those extra interceptions would give a healthy boost (even more so for Bowman, of course).

Also of interest would be the inter-game variance. A catastrophic game from a rookie is to be expected and would certainly be much more preferable than a season of mediocre performances.


To get an idea of the STATISTICAL SIGNIFICANCE of the numbers (critical) -- beyond the facts stated previously -- look at what e.g. Vontae would have to do to move halfway up to the top-10 (so presumably from "pretty much worst" to "pretty much average"): THREE PLAYS moved from the "unsuccessful" column to the "successful" column... over a whole season.

That's pretty ridiculous and clearly shows that in terms of "success rate", at least, there's probably no statistical significant difference between the mean (as in middle-player, not average score which is skewed by a few high results) and the very bottom of the barrel.

by Vincent Verhei :: Sun, 02/07/2010 - 2:51pm

You're doing some math wrong somewhere. Davis had a Success Rate of 43% on 47 targets, which means 20 successes, 27 failures. Moving three plays from failures to successes would mean 23 successes, 24 failures, and a Success Rate of 49%. That would get him out of the bottom ten, but still way short of the top 10 (Leigh Bodden was number 10 at 59%).

by clark :: Thu, 02/04/2010 - 11:01pm

I was expecting to see some Lions, but I guess they went through so many CB's that nobody got 40 targets.

by 4tuna (not verified) :: Fri, 02/05/2010 - 1:33pm

I was expecting the same thing, but I'm guessing they couldn't find anybody to chart Lions games without being paid to watch.

by jedmarshall :: Fri, 02/05/2010 - 11:56am

Kelvin Hayden has subjectively looked worse than last year. He's also been hurt most of the year. That may have something to do with the dropoff from last year.

Of course Tim Jennings is our favorite whipping boy. I am estatic when he actually makes a decent play.

by SteveNC (not verified) :: Fri, 02/05/2010 - 3:15pm

Shocked to see no Steelers on any of these lists.

by Dean :: Fri, 02/05/2010 - 3:46pm

If Bartel had a decent corner on the opposite side and a decent pass rush in front of him, his numbers would be dramatically better. Despite the numbers, he's actually pretty good. Sure, he can be overmatched against the elite WRs of the game, but who isn't? He's not a pro bowl corner, but he's above average.

by Mark Henderson (not verified) :: Fri, 02/05/2010 - 3:58pm

Sure looks like my Saints lucked out in free agency... Greer was the second choice CB -- after Bartell...

by Jamie (not verified) :: Fri, 02/05/2010 - 4:12pm

How was Hole in Zone's season?