After seeing that tackles don’t quite cut it as a raw stat to measure defenders by, there are a number of other defensive metrics that deserve a look as well. Sacks are commonly used to see judge pass rushers, interceptions have been the bottom line for defensive backs, and fumbles forced and fumbles recovered are used for any defensive player.
There is no question that these are all great plays for the defense. The offense loses a down and yards with each sack and interceptions and recovered fumbles put quick ends to possessions. While they are big helps to the team, it’s individuals who are making these plays.
These are pretty much all of the defensive statistics that have historically been kept. They’ve been used to help figure out who should make the Pro Bowl and the All-Pro team and have been used in debates about the greatest players ever, but each can be picked apart as they don’t tell nearly enough of the story on the defensive side of the ball.
Sacks
There are two major things wrong with sacks. First, they only reflect the success of a handful of plays for a pass rusher, and second, they are raw numbers. If you’ve read enough articles at Pro Football Focus, you know we typically give a combined pressure total rather than a sack total when talking about pass rushers. When a defender gets pressure on or hits the quarterback, it clearly affects most passers’ performance. While some quarterbacks are better under pressure than others, I think most would say they’d prefer their offensive line to keep the defense far away.
Of course sacks are better than hits or pressures in that they typically represent a final result and a more successful play for the defense, but pressures happen more frequently and can do a better job of showing the big picture of a pass rusher’s talent. Our numbers show that defensive ends Antonio Smith of Houston, Kroy Biermann of Atlanta, and Brandon Graham of Philadelphia are all very good pass rushers, but you wouldn’t know it just by looking at the three sacks they each had in the 2010 season.
Sacks (as well as hits and pressures) do a good job of showing the number of times a pass rusher made a good play, but like many statistics it’s important to add the context of how often a pass rusher tried to make a play. Our Pass Rushing Productivity metric takes all of this into account and produces a more complete look at who is getting the most done with their opportunities.
Interceptions
Interceptions have the same issues that sacks do, but to a lesser extent, as well as a few other problems. There are plays that defenders can make in the pass game besides interceptions – the most well-known being passes defended – and it’s also important to know how many times a defender went into coverage.
The other problem with using interceptions as a gauge for coverage players is that some are high risk/high reward types, willing to give up a few more big plays for the chance at more interceptions. A classic example is Washington’s DeAngelo Hall whose six interceptions in 2010 tell so little of his story but got him into the Pro Bowl. Hall received a negative coverage rating from us after allowing a 73% of passes his way to be completed and a league-worst eight touchdowns. Terrell Thomas of the Giants, Alphonso Smith of Detroit and Terence Newman of Dallas are more players with significant interception totals (five each) and negative coverage ratings. Interceptions reward these players for the times they get it right, but don’t hurt them when they don’t. The highlights show them making the big plays, so that is typically what people remember of these kinds of players.
One last problem with raw interception totals is that sometimes a player is simply in the right place at the right time. A ball could be tipped and land right in a defender’s hands – ding ding – notoriety and a bigger paycheck are sure to follow. Of course this doesn’t show that a player is a quality defender, just that he was lucky. Considering how few interceptions a defender may get over the course of a season, it doesn’t take much luck to look like a pro bowl player.
Fumbles Recovered
A recovered fumble is great news for the defense since turnovers have such a great correlation with which winning games, but counting them does very little in terms of player evaluation.
While some fumbles are simply the fault of the ball carrier or of a faulty exchange between offensive players, forced fumbles can say something about a defender. Once the ball is on the ground, however, it takes a big luck factor at play. I don’t think you’ll find a metric out there on how good teams are at recovering fumbles. That’s because they don’t say anything worthwhile about the quality of the team, they just hint at how lucky they are. I realize it’s rare to see forced fumbles/fumbles recovered used to evaluate a defensive player, but it is still good to remember why.
Final Thoughts
Defenders have always been difficult to evaluate. When it comes to looking at the historic greats, observers tend to check how many pro bowls the player played in or how often they were elected to an All-Pro team. We don’t put much stock in these teams as they are too often assembled with faulty statistics as support for their inclusion.
There aren’t many metrics to measure defenders, and as we’ve seen with tackles and the rest of the current defensive metrics, those that do exist are lacking. We provide a number of additional stats for defenders and the key behind them all is adding context.
While we can evaluate defenders better now than ever before, it still puts a damper on the past, as we may never truly know how good some of those players were. The play of some that continuously made pro bowls may have dropped off much earlier than commonly believed, and there are probably a number of players that deserved much more recognition than they ever received.
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