by Aaron Schatz

Last week, we ran through the best cornerbacks in FO's game charting stats for 2011. Today, we'll flip that script and look at the lowest-rated cornerbacks according to these metrics.

As usual, the typical caveats about the game charting apply: This is imperfect data based on the game charting project, which means it comes off limited television camera angles, and it is charted by a group of volunteers plus a handful of FO staff members. Sometimes a cornerback will benefit because he happens to be in coverage when a quarterback throws a bad pass, even if he wasn't covering close. Sometimes a cornerback will benefit from a better pass rush, because it's easier to cover when you don't need to cover for six seconds. As we always say, these stats should not be seen as absolute statements on player value. They're just part of the story.

These tables rank all cornerbacks with at least 40 charted passes. I removed all safeties except for Antrel Rolle, who is often playing as a cornerback when the Giants are in nickel (which they are an awful lot of the time). As we do with the cornerback charting stats in the book and on the player pages, 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. However, pass interference is included. No other defensive penalties are included. With defensive pass interference, the defender flagged is almost always the player who was in coverage on the intended receiver; with illegal contact or defensive holding, the flag often comes far away from where an actual pass may be thrown.

We'll start with the cornerbacks who allowed the most yards per pass according to our game charting.

Let's start by cutting Josh Gordy and Justin King a little bit of slack. They weren't supposed to be the starting cornerbacks in St. Louis and were seriously, massively stretched past their limits. Gordy is an undrafted player in his second season, and if struggles for the rest of his career, he can always console himself with the Super Bowl ring he won as a rookie depth corner for the 2010 Packers. Justin King is in his fourth season but didn't start at all in 2010 and was supposed to be the nickelback in 2011 until Bradley Fletcher and Ron Bartell both went down.

Devin McCourty had a huge sophomore slump for the Patriots; he was particularly victimized all year by tall receivers like Brandon Marshall and Vincent Jackson. On one hand, this looks like more evidence of the inconsistency of cornerback charting stats; on the other hand, it's hard to argue that these stats weren't doing a good job of measuring McCourty's actual on-field performance in both 2010 and 2011. He actually wasn't ranked that high in 2010 as a rookie (41st in Success Rate, 38th in Adjusted Yards per Pass) and his 2011 performance pretty much was as poor as those numbers show.

E.J. Biggers is another player who had very different charting stats in 2010 and 2011. In 2010, he was 13th in Success Rate and seventh in Adjusted Yards per Pass. (Adjusted Yards per Pass is the metric we use in the book, after we've had a chance to adjust these numbers for which receivers each cornerback was covering on each pass.) You might think that's Biggers getting exposed by more time on the field, but we have him down with 68 targets in 2010, so he wasn't used that much more than in 2010. Also, in both years I believe he generally played on the outside because Ronde Barber moves to the slot when the Bucs go nickel.

Leodis McKelvin has interesting numbers, with a terrible yards per pass number but a fine Success Rate. You'll get that kind of thing with a lower sample size. (He's only one pass above our minimum to be ranked.) We've got McKelvin giving up five different passes of 40+ yards: 58 and 40 to A.J. Green, 50 and 42 to Denarius Moore, and 42 to Santonio Holmes on a DPI. Those weren't big YAC passes -- each one was at least 34 yards through the air. So when McKelvin did get beat in 2011, he got beat badly. On the other hand, our charters gave McKelvin a pass defensed on eight of the 40 passes where he was listed as the main defender in coverage, which is a pretty good ratio.

Quentin Jammer has never really lived up to his rep, if our charting stats are to believed. Terence Newman is toast.

Next, we'll look at the worst cornerbacks in Success Rate. 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.

Oh, hey, there's DeAngelo Hall. We knew he would show up somewhere around here. The Minnesota cornerbacks really were god awful in 2011, except for Antoine Winfield when he was healthy.

Tracy Porter from New Orleans had similar numbers in 2010, with a better rank in yards per pass than in Success Rate. In 2011, we have Porter down giving up a completion or DPI for 8-20 yards on 30 of his 63 charted targets -- but he gave up only one pass that gained more than 20 yards, a 47-yarder to Nate Burleson. Part of the reason for this is the way he was used by New Orleans, as we only have him down in coverage on seven passes that went 20 or more yards through the air. Indianapolis cornerbacks like Jacob Lacey, who are used in a similar fashion, also end up with this kind of low Success Rate/low yards per pass combination.

On the other hand, compare Porter to Jabari Greer. We have Greer down with 94 targets, about 50 percent more than Porter. Yet Greer only gave up 23 different passes that gained 8-20 yards either by completion or DPI. Of course, Greer also allowed eight passes that gained over 20 yards. But Greer ends up with fewer yards per pass allowed (6.9) with a far better Success Rate (61 percent).

Finally, let's look at Yards After Catch:

Now, let's be clear: These YAC allowed numbers generally don't say much about the actual quality of a cornerback. There's generally very little correlation between a cornerback's rank in Success Rate and his rank in YAC allowed. Still, it is very strange to see Champ Bailey giving up the most average YAC of any starting cornerback in 2011 -- and by a wide margin. Isn't he known as an excellent tackler for a cornerback? Yes, and there isn't much evidence that this is an issue of tackling. We only recorded Bailey with two broken tackles on plays where he was in coverage. He just seemed to have a few more plays than usual where guys got behind him on short- and mid-range routes. We have Bailey down in coverage on five different passes that gained 18 or more YAC. The big one there is a short cross to Percy Harvin in Week 13 that went for a 48-yard touchdown with 46 YAC, thanks in part to a broken tackle by third-string safety Kyle McCarthy. We've also got a 56-yard touchdown to Calvin Johnson (25 YAC), 34- and 31-yard passes to Jacoby Ford (23 and 21 YAC), and a 30-yard pass to Plaxico Burress (18 YAC).

Full charting numbers for cornerbacks, including numbers adjusted for opponent, will run in Football Outsiders Almanac 2012.