The IDP Metric System: Passes Defensed and Interceptions

If you’ve played in IDP leagues with defensive backs, you know very well the frustrations of finding a consistent defensive back. Many times we get our hands on a hot player only for him to fizzle out just as quickly as he exploded onto the fantasy scene.

Now you see me. Now you don’t.

This conundrum is one that most IDP gamers face at multiple points in a given season. The simple fact is there are very few consistent options at the position, so it’s a good idea to grab an elite option on draft day. From there, it’s often a game of DB roulette for the rest of the season.

However, there are ways to get ahead of the curve and identify productive defensive backs. In most leagues where tackles dominate IDP scoring, your best insight comes from looking at tackle frequency. Using this metric, here are the top-25 defensive backs from 2012:

We have seven cornerbacks and 18 safeties on the list, though it should be noted that Corey Graham played 90.3% of his snaps at cornerback. Of the corners, only Finnegan and Winfield weren’t nickel corners last season. However, in the nickel packages Finnegan saw a lot of his time in the slot. In fact, 51.3% of his snaps on the season came in the slot. Winfield was used even more heavily as a slot corner, with 57.1% of his snaps coming there. In the pass-heavy NFL, nickel corners can be quite productive and, as a result, have become increasingly viable fantasy commodities that are worth consideration in the right matchup. 

Of the safeties, Jordan Babineaux and George Wilson top the list. Interestingly, Wilson recently signed with the Titans and will be replacing Babineaux. While Wilson’s stock dipped last season after a soured relationship with the Bills’ coach staff, he’s an interesting name for 2013 in what has historically been a very productive spot. Babineaux’s path is much more up in the air, though it’s fairly certain he won’t be back with the Titans. Based on his track record, it’s tough to recommend owning Babineaux going forward unless he lands in an ideal situation. 

From here, much of the list reads like a who’s who of IDP safeties, with a number of my preseason top-20 defensive backs. Of course, there are a few outliers like Danny McCray, Atari Bigby, Kurt Coleman, and Erik Coleman. All four produced in volume due to their roles last season, though I’m not sold on any of them assuming a starting job in 2013.

Indeed, tackle frequency serves as a solid metric for defensive back evaluation in tackle-heavy leagues that lump safeties and corners together. But how do we evaluate defensive backs in cornerback required leagues and/or big-play leagues?

Here, our approach needs to take more statistical categories into account. In particular, I suggest we focus on interceptions and passes defensed (if your league doesn’t score passes defensed, you should start). Interceptions are unpredictable, but like sacks, players can increase their chances of recording one by putting themselves in the right position.

A good gauge of whether or not a defensive back is consistently in a position to intercept passes is to take a close look at their passes defensed. As I’ve discussed before in this series, it’s misleading to just look at the raw number. Instead, we need to consider how disruptive the defensive back is on a per target basis. To do so, we simply add a player’s passes defensed and interception total, then divide this number by the amount of targets thrown into a player’s coverage. I call this metric a Pass Defensed or Interception Frequency (or PDI). 

A player’s PDI gives us a good indication of their big-play upside, and this can be an extremely useful tool in identifying corners to target in CB-required leagues. Of course, we want to identify players who not only have a high PDI, but also see a lot of targets thrown into their coverage. The following list contains the top-25 PDIs among CBs who saw at least 50 targets in 2012:

There are a number of players on this list who recorded strong PDIs, but had less than 50 total tackles. Some, like Darius Butler and Leonard Johnson did not play in all 16 games. Others were subpackage specialists, like Tony Carter and Chris Culliver. The remaining players – Asante Samuel, Leon Hall, Ike Taylor, and Brandon Flowers – are strong in coverage, but do not typically produce high tackle numbers. We can throw all of these players out. I’m also going to toss Nnamdi Asomugha, Jabari Greer, and Kareem Jackson, all of whom just barely cracked 50 total tackles and were targeted on roughly 15 percent or less of their snaps in coverage.

We’re now left with 14 names. Richard Sherman and Casey Hayward tower over the pack with a pass defensed or interception on more than 36 percent of the passes thrown into their coverage. While it may be unreasonable to expect either to repeat their interception totals, these guys are serious ball hawks. Both also topped 50 total tackles, which makes them viable fantasy starters. Sherman and Hayward should be top priorities in big-play CB-required leagues in 2013.

In IDP circles, it’s no secret that Patrick Peterson and Tim Jennings offer huge big-play upside. Their PDI numbers certainly support that reputation. Dominique Rodgers-Cromartie falls just behind Peterson in terms of PDI, but his tackle numbers are on the lower side of things. Still, his upside is appealing. He’s worth a late-round flier in deeper CB-required leagues.

IDP stalwarts, Jason McCourty and Charles Tillman also make the list. Both Tillman and McCourty are part of just a handful of corners that you can get away with starting in non-cornerback required leagues. With extremely strong tackle numbers and high PDIs, both are elite options in all fantasy formats.

The Ravens are well represented here with both Cary Williams and Corey Graham making the cut. Graham’s 61 total tackles in the regular season is particularly impressive considering he didn’t assume a significant role until the Ravens’ Week 10 win over the Raiders. With Williams likely to walk in free agency, Graham is especially intriguing if he get’s the nod at right corner opposite Lardarius Webb.

One final name from this list that deserves our attention is Stephon Gilmore. In his rookie season, Gilmore played all but 34 of the Bills’ defensive snaps and was targeted 98 times. His 61 total tackles isn’t a jaw-dropping number, but it’s more than respectable production. That coupled with his PDI of 19.5 percent makes Gilmore an interesting fantasy option for CB-required leagues. 

Just as we saw with QB pressure frequency and tackle frequency, we can’t use PDI exclusively in player evaluation. However, PDI is a solid supplement to other metrics that provides a good indication of a player’s big-play upside.

Jeff Ratcliffe is the Senior Editor of IDP Content for Pro Football Focus Fantasy. Follow him on Twitter – @JeffRatcliffe