What has been the key to the Chicago Bears defensive success this season?

In recent years, the Bears have primarily played a split-safety Cover 2 formation with two defenders in the secondary. This season, they have utilized a single-high safety with fantastic results.

A single-safety defense is defined as one that has one safety deep in pass coverage. The split-safety defense is defined as two safeties ‘split’ deep in coverage.

The idea behind one deep safety as the last line of defense is that the second can be used at the line of scrimmage. It’s important to have cornerbacks who can cover 1-on-1 downfield for a single-safety defense to be effective. Tim Jennings has done just that for the Bears, leading the league with five interceptions on throws more than 10 yards downfield, including three when they are in single-safety coverage.

Let’s take a look at what our video review showed on the Bears defensive excellence. We broke down every coverage used by the Bears excluding penalties, spikes, a fake punt and plays inside the 10.

What the numbers show...

The Bears have balanced their secondary coverage, using a single-high safety on slightly more than half of the pass attempts.

With the Bears having played several blowouts, it’s important to note that when the score has been within one possession, the Bears prefer single-safety coverage on 64 percent of pass attempts.

The Bears single-safety defense is holding opposing quarterbacks to a much lower completion percentage (-14.4 percent) as noted in the chart on the right.

The most noticeable impact is in the short passing game, where the Bears single-high safety has held opponents to a 59 percent completion rate on throws 10 yards or fewer, with five interceptions and no touchdowns.

Their split-safety defense has allowed nearly 75 percent of such throws to be completed.

Looking ahead to Monday Night

The last time Chicago and the San Francisco 49ers met, the Bears "loaded the box" on nearly half of the defensive plays (45 percent), their fourth-highest single game percentage in the last four seasons. In that contest, 49ers quarterback Alex Smith was sacked twice and threw his only interception against a loaded front.

No team in the NFL has used a “loaded front” on defense more often than the Bears (28 percent of plays). A “loaded” box is identified when the defense has more players in the ‘tackle box’ than the number of available blockers on offense.

While evidence suggests Chicago will utilize the single-high formation and load the box often on Monday, they might want to be weary of Colin Kaepernick’s strong arm. His average throw has traveled 10.5 yards downfield this season, the furthest in the league among quarterbacks with at least 20 attempts.

The 49ers backup has completed seven of 10 attempts traveling more than 10 yards downfield in his limited time this year, while the league average completion percentage on such throws is 48.9 percent.

Kaepernick could challenge the Bears loaded front downfield, but it should limit his scrambling. He has been quick to run this season, scrambling on seven of his 38 dropbacks (18.4 percent), the highest scramble rate in the league (minimum 10 dropbacks).