By the Numbers: How much did the Bears defense improve?

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With most of the big free agent signings already over with and team’s focusing on the draft, it’s worth wondering how much better the Bears are right now than when they concluded the 2013 season.

At least one famous Chicago writer speculated that the Bears aren’t really much better at all. Chicago Football’s Hub Arkush doesn’t think Lamarr Houston is an upgrade over Julius Peppers or that Willie Young isn’t better than Corey Wootton.

Arkush uses only raw statistics for his thinking, which would be fine a decade ago. It’s 2013, there is currently more information available and the numbers strongly refute Arkush’s thoughts.

We can start with the run defense, where Peppers and Wootton made up half of the defensive line for what was by far the worst run defense in the NFL.

Last season, the Bears ranked 14th on runs around the left and and 28th on runs over the left tackle, according to Football Outsiders’ Adjusted Line Yards statistics (rushing yards adjusted for down, distance, opponent and other metrics). Those would be the spots Peppers is responsible for defending.

Wootton played primarily on the left side of the Bears line—right side for opposing offenses. The Bears were ranked 32nd on runs up the middle, 29th on runs over the right tackle and 19th on runs to the outside.

The Bears higher rankings on runs to the outside have quite a bit more to do with their fast linebackers. Even though Jon Bostic, Khaseem Greene and James Anderson all struggled to shed blocks, they were able to get sideline-to-sideline.

On Peppers’ side, the Bears gave up 4.09 ALY and they gave up 4.335 to the other side.

With Houston playing the left side, the Raiders gave up  an average ALY of 3.65 on runs to the left side, ranking 11th in runs around the left and and 13th on runs over the left tackle. Young’s average was even better at 3.44, as the Lions ranked fifth on runs to the right tackle and 20th on runs outside. 7.09.

Added together, the Bears run defense the Bears’ run defense improved by nearly 1.5 ALY. If you prefer raw numbers, the Raiders had the 13th best running defense, while the Lions had the sixth best. Both were key factors in their abilities to stop the run.

That’s just one part of the equation.

During his press conference, after he introduced Houston to the media, Emery spoke about his value as a pass rusher.

While the old-school thinking is that sacks are king, there’s more to the story as Emery detailed. He usually speaks about disruptions, and he provided some clarity to that last week.

“From 2008 on, when a pass play is performed without pressure, knockdown hit or sack percentage of completion is about 64 percent,” Emery said. “When there’s a sack, obviously it goes to zero, but with a hit or a pressure it goes to 38.5 percent.”

Using data from the snap counts on Pro Football Focus, combined with the averages Emery used, opponents would have had an average completion percentage of 61.2 percent when Peppers was on the field and 62.1 percent with Wootton.

Now, since Wootton spent some time in an unfamiliar spot, playing defensive tackle, that may not be the best way to judge. Even if you were to go back to 2012 when he was a full-time defensive end, the completion rate is 61.1 percent.

While Houston and Young have had less sacks than Peppers and Wootton, they’ve been more effective pass rushers.

The completion percentage for Houston would be just 60.1 percent, while Young is at 60.9 percent.

While those end numbers may not be significant differences, consider this. Peppers failed to get any pressure on 91.2 percent of his pass rushes, Wootton didn’t sniff the quarterback on 93.3 percent of his. Both Houston and Young were under 90 percent, they combined for 123 quarterback disruptions while the Bears former defensive end duo had just 72. Considering each disruption decreased the quarterback’s odds of completing a pass by over 25 percent, you can see how that adds up.

With a significantly better run defense, the Bears should have opponents in more long-distance situations, further increasing their chances of forcing an incompletion.

Perhaps if it were Houston rushing instead of Peppers, he would have hit Aaron Rodgers on his game-winning bomb to Randall Cobb, forcing an incompletion and winning the NFC North for the Bears.

These are the kinds of things that add up and make a difference in wins or losses throughout the season, especially at big times in big games.

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  • kurt

    This article on how much the Bears defense has improved with the new additions on the defensive line is an absurd attempt to prove with statistics that the Bears change of players will make a substantial difference this year. What has not been considered is the fact that the top two 3 technique tackles were missing for most of the year, and the linebackers for the Bears were missing in action also, especially up the middle.Peppers and Wooton played hurt for most of the season, and were constantly attempting to beef up an absurdly undermanned line. They gave a valiant effort, but no team can look good with two players trying to cover for seven. The two new signees had experienced and accomplished line members to support them. The Bears will miss Peppers and Wooton.

  • Kunis

    What everyone needs to remember is we only need a good Defense . Not a great Defense. Jay Crew will average 32 points this year . Watch and see. Bear Down

  • Mr.Vic

    Getting rid of Mummy Peppers is an improvement and wooton well dont think the Bears will miss him either. Defense is much improved now im excited.

    • Jon freed

      Wootton is at best an average lineman-nothing special. Peppers may have some mileage left in him, but he sure did not show it last year. At a time they really NEEDED him to step up-he didn’t . What’s important is the fact the both Houston and young have the prime of their careers ahead of them. So far, I think Emory has done as well as he could with the cap space he had to work with, and put himself in a good position to be a bit flexible for the draft. They should be able to sign a solid D-lineman or two, and a solid safety. Once those are “in the bank”, I’m sure he has a number od “best players available” he likes.