The concept of possession has been long debated in the NFL; If a team spends more time possessing the football, it's said they'd be the most likely to win. However, this was largely debunked in a series of famous—or infamous, depending on which side of the trenches you were on—games and now the focus is on forcing turnovers, which is the concept of stealing possessions.
The Bears are quite good at stealing possession, accumulating a mind-boggling 30 takeaways this season through only 10 weeks. This is arguably the greatest reason of them all as to why they're the most dominant defense in the NFL but it's not the sole reason.
Chicago employs one of the least diverse, yet most effective schemes—Tampa-2—and are excellent against the run and pass because of their fierce pass-rush and outstanding linebackers.
For starters, their brutish run defense has stood out on many occasions this season and for the majority of the weeks has not allowed grand rushing games to ball-carriers. Most recently against the Houston Texans, they allowed 102 yards to All-Pro running back Arian Foster but only 3.5 yards per carry.
Houston's running game was equivalent to trying to run around the endless Great Wall of China.
An instance of the the Bears' dynamite run defense came early in the game when Houston had possession in Chicago's territory. Houston came out in a one back set with a single tight end lined up to the right end of the offensive line.
Chicago, who operates out of a few fronts, was aligned in their popular "Under" front, featuring a 1-technique nose tackle on the strong-side of the formation and a 3-technique under tackle on the weak-side of the set.
At the snap, Texans' running back Arian Foster received the ball and stretched the ball to his left, where defensive end Julius Peppers stood.
Peppers was one of the defenders whose primary job was to flatten the edge of the defense in order to force Foster to keep running parallel to the line of scrimmage.
While Peppers was doing this, the rest of his teammates either penetrated up the field, which is the key to defending zone stretches, or flowed in the direction of Foster with discipline, maintaining their assigned gaps and ending any possibility of a cutback lane being recognized.
As Foster ran and scanned the field, the real estate he once had was quickly shrinking, forcing him to continue wide and through the B-gap between the tackle and guard.
Finally, he ran out of room and had nowhere to go but out of bounds, where he encountered Julius Peppers and received a slight push from.
Chicago's picket-fence defense was significant on this play, forcing Houston to stretch their runs wider than they'd prefer and struggle to establish a running game.
While the run defense has been excellent, the pass defense just might be better.
It's a very interesting pass defense because of the coverage concepts the Bears run, which consists of a few (such as Cover 3; pictured in white) but most notably their Cover 1 (Man-Free) and Tampa 2 coverages.
Cover 1 (in orange) is the man concept of the two, assigning all but one (sometimes two) defenders to a receiving threat while the remaining defenders play zone and look to undercut routes in hopes of forcing a turnover.
The benefits of this coverage include the ability to get enough numbers in the box to defend the run while also accounting for potential pass threats.
Conversely, Tampa 2 is a pure zone coverage, relying on its defenders to get to their landmarks (assigned areas) and keep all 11 eyes on the quarterback while keeping the pass catchers in front of them.
One big difference between this coverage and Cover 1 is that turnovers are more frequent because defenders don't have their back turned to the ball as often. Further, it forces antsy quarterbacks and offensive coordinators to be patient moving the ball, which doesn't happen often and usually results in turnovers.
Another benefit of zone coverage, especially the Tampa 2, is that it allows defenders like cornerback Charles Tillman to punch out the ball to force a turnover. Tillman has gained nationwide popularity in recent weeks for his use of fists and for good reason—he's forcing plenty of turnovers. This season, Tillman has forced seven fumbles, including four against the Tennessee Titans in week 9.
The first of the four forced fumbles came on the first play of the game when Tillman stripped Kenny Britt after what appeared to be a first down pickup.
When asked about it, Tillman revealed he learned the art at Belton High School on "Turnover Tuesdays," as detailed by David Haugh of twincities.com.
The Ragin' Cajuns' stat sheet credited Tillman with 20 tackles, nine solo, suggesting he made many plays downfield on receivers who had caught passes. On several Wofford receptions in front of Tillman, Southern recalled the cornerback "was coming in from behind or the side and they had the ball exposed where he could have punched the ball out."
He didn't. So after the game, Southern simply shared his observation in a playful way.
"He came to a game and he told me, 'You know, you could have forced a lot of balls out if you could just punch it,' " Tillman recalled in Nashville, Tenn., pausing slightly for effect. "Light bulb!"
Along with the great punching skills of Charles Tillman, the Bears' "Under" front controlling offenses' running games and the Tampa 2 and Cover 1 concepts passing games, Chicago has developed a defensive squad that is arguably the most dominant in the NFL.
They do it on a consistent basis, which is the key to their dominance.