2012 Dallas Cowboys Free Agent Cornerback Primer: Finnegan, Grimes, Carr And More

Free agency will not officially begin until the start of the new league year in March. But over the next days and weeks, you'll be hearing all sorts of speculation, whispers and rumors about which players the Cowboys could conceivably be targeting in free agency.

Cortland Finnegan, Brent Grimes, Brandon Carr and many more names will pop up as potential candidates for the Cowboys' secondary. To help you stay on top the who's who in the cornerback market, we've compiled a little free agent cornerback primer with key stats for all the free agent cornerbacks who played at least 25% of their teams' snaps in 2011.

After the break, we look at the top 20 free agent corners, how they held up in pass coverage and how they ultimately graded out.

Obviously, stats are not the only thing that counts in evaluating free agents. But stats do help a little to form a picture of a player you may have never heard of, or whom you've never watched play.

All of the stats below are highly contingent upon the scheme, position, number of snaps, type of defense and many other variables that affect a players' numbers. Just because one guy has a better defensive passer rating (to use just one example) than another guy doesn't automatically make him better. So don't take the rankings as gospel, rather, use them as an orientation as you navigate the Cowboys' options among free agent corners.

Free agent corners in pass coverage

Quick explanation of the stats we'll use below:

Burn rate: number of catches a corner allows versus the number of balls thrown at the receiver he is covering. For example, a burn rate of 80% would mean that opponents have completed eight of ten passes thrown at the receiver the cornerback is covering. The lower the number the better.

Defensive Passer Rating (DPR): uses the same data and formula used for the passer rating for the quarterback (i.e. completion percentage, yard per attempt, touchdowns and interceptions), but applies them to a defender, where they become completion percentage allowed (aka 'burn rate'), yards per attempt allowed, touchdowns allowed and interceptions made. The lower the number the better

NFL rank: DPR ranking among 109 corners who played on at least 25% of their teams' snaps in 2011.

"Burn Rate" is a stat that is often discounted with an argument favored by Asomugha apologists: A player is "so good" that opposing offenses are simply not throwing his way. A look at the numbers should clear that right up.

On average, the 109 corners in this analysis were target on 9.3% of their defensive snaps. The lowest value with 4.9%, is indeed held by Nnamdi Asomugha, closely followed by the Rams' Bradley Fletcher with 5.6% (whom nobody will confuse for a shut-down corner) the highest value is 15.1%, held by the Jets' Donald Strickland. So yes, there are differences in number of targets per corner, but these depend on a lot of factors, only one of which is the quality of the corner in question.

In any case, the much more important question is how successful a given corner is once he's targeted, and the Burn rate answers that question. A burn rate below 50% is an excellent value for a corner in today's NFL.

Of the starting corners in the league, the Jets' Darrelle Revis (41.2%) and the Steelers' Ike Taylor (41.7%) led the league. Asomugha (61.7%) ranks 68th among all 109 corners in this analysis. To put that rate in context, Mike Jenkins (51.9%, 22nd) and even Alan Ball (60.8, 63rd) are better, with Terence Newman (62.8%, 74th) only slightly off the pace.

Overall 2011 Corner Grades

We'll use the Pro Football Focus grades for this second exercise. Once again, just to make sure we have the definitions right:

PFF Grades: PFF look at game tape, assign a grade for every play and then ‘normalize’ the data so that the average player for a given position is graded at zero. The higher the positive grading the better the performance and vice versa.

However, these grades are cumulative. Say you have two players who consistently are graded with a +1.0 per game. However, one is injured after eight games, the other plays the full 16 games. The result: one player gets a +8.0 for the season, while the other gets a +16.0 although they basically played the exactly the same.

Expected Points Added EPA for 2012 free agent corners:

Expected Points Added: EPA is a metric developed by Brian Burke at Advanced NFL Stats. It measures the impact a given player has on a given play by comparing the result of the play to the league average results on plays from that down and distance (details here). The result is calculated as expected points a team would score as a result of that play. The higher the value the better.

Because this stat measures the impact per play, the more plays (or snaps) a corner has, the higher his EPA will be. So in addition to EPA/game, I've added EPA/ 100 snaps to normalize that effect.

Rank indicates position among 163 NFL corners.

There are a number of further free agents that are not included in these lists, some of them on the verge of retirement (Ronde Barber, Bucs) some of them coming off injuries (Terrell Thomas, Giants).

Alan Ball and Frank Walker are free agents, and Terence Newman is likely to have played his last season as a Cowboys. The draft will not be sufficient to provide the type of depth the Cowboys will need at corner next season, so a free agent or two will have to be brought in.

Now that you have all this data, who do you think the Cowboys should go after, and are there candidates here that you haven't thought about before?