Pro Football Focus is known for their thorough game data, with a collection of stats that examine football in greater depth. They keep stats for the amount of quarterback hurries, hits, and sacks created by each defender. Recently, they took a look at the success rate for pass rushers finishing off their pressures with sacks. Their study, which examined career numbers for every player since 2007, found that edge rushers generally create sacks at a higher percent than defensive linemen.
The leaderboard was populated by familiar names like Joey Porter, Elvis Dumervil, Justin Houston, and Jared Allen, while the rear included some notable disappointments like Jamaal Anderson, Robert Geathers, and Brooks Reed. One interesting note, which we'll dive into here, was the appearance of Marcell Dareus in the top tier of defenders - not just defensive linemen, but all defenders.
Dareus turns pressures into sacks better than almost anyone in the league. That being said, he's not among the league leaders in pressures generated (that's a job better suited to edge rushers). So how useful is that stat PFF looked at?
On the one hand, there's a school of thought that says that generating pressure is more important than finishing off the play. If an offense is constantly on its heels because it has to deal with unexpected pressure, it will eventually be forced into a mistake. On the other hand, you have the more conservative viewpoint: a play doesn't matter unless it's fully finished. A sack actively hurts the other team's chances to continue a drive, while a pressure may have no impact on the outcome of a play.
Different schemes value different approaches. Examining roster building from an analytical perspective, a Rex Ryan defense values pressure and confusion above all else. For them, the most important stat would just be the amount of pressure a player generated, regardless of outcome. Looking at things from a value perspective, a team might look for players who had a slew of quarterback hurries and hits in previous seasons, but didn't put together big sack numbers, hoping they could sign him to a smaller contract and have him turn those hits into sacks in future seasons.
The question is, to what extent can a player control his success converting a pressure into a sack? Is it a natural ability? A skill that can be learned? Or is it just luck?
Let's take a closer look at three defensive linemen to feel out the year-to-year fluctuations of these stats: Dareus, Kyle Williams, and J.J. Watt. The following graphs look at the last four years of production from each player; Williams is omitted from 2011 after he missed all but five games due to injury.
One thing is clear here: Watt is a freak of nature; he generates pressure at double the rate of Dareus. Think about that for a second.
We can see that this performance is (relatively) consistent between the three players. Dareus, Williams, and Watt each sit in different tiers of pressure generation. Some of that is due to skill, and some due to scheme. Both Williams and Dareus are dangerous pass rushers, but Dareus takes on multiple blockers more often than Williams, which gives him fewer opportunities to easily generate pressure.
Sacks have a bit more fluctuation to them. Watt is one of those rare players capable of generating 20 sacks in a season, but that's still difficult to consistently do. As Bills fans, we have seen plenty of fluctuation in pass rushing productivity; from Mark Anderson's phantom season following an 11.5-sack year, to Jerry Hughes' sudden breakthrough as a pass rusher after unproductive years backing up Dwight Freeney and Robert Mathis.
Where Dareus stands out from the rest is his efficiency in finishing off his pressures with a sack. His productivity has steadily increased in each year of his career, while his amount of pressures remained roughly constant, and there is no defensive lineman with a higher percentage of pressure that turns into sacks. The conversion percentage stat appears to be more volatile than the general amount of pressures, with the way players like Watt can fluctuate between 15-37 percent depending on how many sacks they can net.
When thinking about pass rushing efficiency, it may be best to treat it like baseball's BABIP (Batting Average on Balls in Play). In baseball, a batter can't reach base if he strikes out (barring a dropped third strike), but if he puts the ball in play, his chances of reaching a base will depend on what happens to that ball. Some outcomes from a batted ball depend on luck, some on defense, and some on skill. Likewise, every pass rushing snap is like an at-bat for a defender. If he manages to win his matchup and pressure the quarterback, he "made contact with the ball." Whether he finishes off the play comes down to his individual skill (does he have the burst and combat skills to bring down the quarterback in time?), his opponent (is the quarterback mobile enough to escape the pressure?), or just plain luck (did he trip over a player trying to turn the corner?).
Watt is like the Tony Gwynn of pass rushing. He rarely "strikes out," and he puts so many "balls in play" that he is capable of putting together amazing statistics, if his luck lines up. Dareus is like Derek Jeter, who had one of the highest career BABIP in MLB history. While he's not generating nearly as much pressure as Watt, he's excellent at "getting on base" once he's started a play, through a combination of picking good situations to generate pressure, and having the burst to suddenly reach the quarterback once he defeats a block.
BABIP can fluctuate, and so will pass rushing efficiency, but in combination with other knowledge (for example, the amount of pressures generated relative to the number of snaps played), they provide useful information for evaluating pass rushers. As the data shows, Dareus is a rare beast on the defensive line, and it'll be enjoyable to continue following his development in the upcoming season.