Adjusted Sacks and IDP Regression

There’s been a lot of talk about sacks over the last few weeks. Aldon Smith of the 49ers wants the sack record, but said he wouldn’t “punch himself in the face” if he doesn’t get it. Panthers DE Greg Hardy said his personal goal is 50 sacks this season, but he had no comment on self-inflicted face punching.

Hardy’s lofty goal is more than double Michael Strahan’s single-season record of 22.5 sacks. While I admire his ambition, it’s obviously an impossible feat. But Strahan’s record is certainly within reach. J.J. Watt, Aldon Smith, and Von Miller all made serious runs at the record last season, and Jared Allen came up just a half-sack short in 2011. 

These inflated sack numbers have really intrigued me. However, as someone who’s constantly looking at defensive player statistics, I can tell you that the raw numbers rarely tell the whole story. I've talked about this problem before with QB pressure frequency, but this metric still doesn't give the depth of analysis we need to truly understand sack production.

To get a sense of how pass rushers produce, I put last season’s sack numbers under a microscope. In my analysis, one question kept popping into my head: How would defensive ends and rush outside linebackers produce in a vacuum? In other words, some players recorded sacks more frequently than others. What ultimately was the average conversion rate, and how would last season’s sack totals change if we apply the same conversion rate to everyone’s sack totals?

In order to determine the answers to these questions, I first conducted a five-year study where I looked at the QB pressures (the sum of sacks, hits, and hurries) accumulated by defensive ends and rush outside linebackers. I then calculated the sack conversion rate by dividing the sack total by the QB pressure total.

The above data gives a solid sense of the league-wide trends among the pass rushers. Generally speaking, we’ve seen an increase in sack conversion rates over the last five years. While our sample size isn’t massive, 2010 does seem to be a bit of an outlier. The 15.6 percent conversion rate is nearly a full percentage point lower than the five-year average of 16.5 percent.

Now, with this data we can get to work adjusting last season’s sack totals. Remember that the goal here is to see how every pass rusher would perform on an even playing field. We accomplish this parity by assuming that all players convert their QB pressures for sacks at the same rate. This means applying the five-year average of 16.5 percent to each player’s pressure total from last season. The following displays all defensive ends and rush outside linebackers who recorded at least 10 QB pressures last season:

It’s immediately apparent that the sack totals at the top are much lower than what we actually saw. Cameron Wake and Von Miller top the list with an adjusted sack total of 14.2, which is significantly less than Watt’s actual total of 20.5 sacks. This means we obviously have some overachievers in the bunch. Here are the most notable overachievers who saw significant snaps last season:

Watt tops the list, converting nearly 27 percent of his pressures for sacks. He’s followed closely by Smith, who recorded a sack on almost 28 percent of his pressures. The rest of the adjustments aren’t as significant as Smith’s and Watt’s, though a number of these players will garner strong consideration in IDP drafts this season.

So what about the other side of the coin? Let’s take a look at the notable underachievers:

Derrick Morgan tops the list, and his adjusted sack total of 11.9 should give you a strong sense of why many IDP analysts have pegged Morgan for a breakout in 2013. Morgan’s teammate Kamerion Wimbley also underperformed recording a sack on just 10.3 percent of his pressures. Likewise, Lamarr Houston’s low conversion rate of just 8.3 percent should regress upward toward the mean. He’s a sneaky value in fantasy drafts this season.

Further down the list, Ryan Kerrigan had an impressive 69 pressures. He’s an extremely talented pass rusher who is still flying under the radar. Snatch him up if you're in leagues with big-play scoring systems. We also see a few notable underachievers on the list including Jason Pierre-Paul, Carlos Dunlap, and Jason Babin. But what do we make of their underachieving?

Can adjusted sacks be predictive of regression toward the mean?

So far, we’ve taken a look at last season’s adjusted sack totals, but what about the totals from previous seasons? Does the adjusted sack total give us a better sense of future performance, or are some players just better at converting sacks than others?

The answer to this question is certainly complex, and I always recommend closely watching game footage to get a sense of how effective a particular player is as a pass rusher. There's no doubt that some are going to be better than others. At the same time, the numbers can be very insightful.

I’m not going to do a full regression analysis here, though that may be the topic of a future piece. Instead, let’s focus on the sack leaders from previous seasons. We’ll adjust their sacks and then compare that total to what they did in the following season:

Among the 2011 leaders, Smith was the only player who did not drop off last season. The conversion rate from the other four players regressed toward the mean, with Babin and Pierre-Paul being the most significant examples. Let’s also take a quick look at the sack leaders from 2010 and what they did the following season:

Again we see four-of-five players regress in the following season. Interestingly, Hali was second in the league and actually underperformed based on his pressure total. The only player to again overachieve in the following season was Ware, though we did see a regression from him in the 2012 season.

While this is just a snapshot look at the data over the past three seasons, one fact rings true – sacks are difficult to come by. When we evaluate and project pass rushers, it’s unreasonable to expect most of them to overachieve. Sure, there will always be players who outkick their coverage. But to expect them to maintain this level of production from one season to the next is completely unreasonable.

As adjusted sacks display, the raw sack number can mislead fantasy owners and create expectations for future production that are unlikely to be met. Like sacks, QB pressures alone don't tell the whole story. But when used in conjunction with sacks, the sack conversion rate is a much more effective weapon in your IDP arsenal. While a pass rusher may not be precisely at the mean conversion rate, this frequency will give you a much more realistic sense of what to expect out of your defensive ends and rush outside linebackers.

Jeff Ratcliffe is the Assistant Managing Editor of Pro Football Focus Fantasy. Follow him on Twitter – @JeffRatcliffe