The Colts relied heavily on the "Tampa-2" or cover-2 defense during the last decade having been implemented during Tony Dungy's eight year run followed by Jim Caldwell's two years as head coach.
Caldwell was fired at the end of last season and the Colts hired former Baltimore Ravens defensive coordinator Chuck Pagano to be their next head coach. Pagano brought to Indianapolis the 3-4 defense and a plethora of moves to the defense.
Despite a change in defensive philosophy, the Colts two most important players are Freeney and Mathis. Both Freeney and Mathis have been transformed from 4-3 defensive ends to 3-4 outside linebackers.
The Colts have shown in the preseason that they are not using a traditional 3-4 defense and often times both Freeney and Mathis have found themselves lining up at the end position with a hand in the ground.
Regardless of whether Freeney and Mathis are playing as a stand up 3-4 backer or with a hand in the ground at the end position, both are causes for concern for the offensive line and Jay Cutler. Freeney is best known for his spin move while Mathis is known more as a bull rusher.
Left tackle J'Marcus Webb will have his hands full all day with Freeney while right tackle Gabe Carimi will be seeing a lot of Mathis. In order for the Bears to properly shut down the two outside linebackers, they will have to attack them. Forcing them to stop the run or trying to have them match up with a tight end running a route will be the Bears best plan to stopping their pass rush.
One of the biggest moves during training camp was the Colts acquisition of Dolphins' former first round pick, Vontae Davis. Davis is big, physical cornerback who will likely get matched up with Brandon Marshall on Sunday.
Marshall's best chance to beating Davis will be his speed. With a less than stellar secondary, the likely double teaming of Marshall will also pave the way for other receivers like Earl Bennett, Devin Hester, and Alshon Jeffery to produce.
The biggest blow to the Colts defense this preseason was the loss of last year's leading tackler, Pat Angerer. Angerer was injured in the preseason opener against the St. Louis Rams and is expected to miss at least a couple more weeks with a broken foot.
To replace Angerer at the inside linebacker position is Jerrell Freeman. Freeman, who signed with the Tennessee Titans as an undrafted free agent in 2008, has spent the last four seasons in the CFL before getting a chance to fight for a spot in training camp with the Colts.
Look for the Bears to attack Freeman in the middle of the field by running the football up the middle as well as bringing wide receivers and tight ends across his face.
With so many new changes to their defense, the Bears should be able to exploit the weaknesses that are clearly there for the Colts.
Despite all of their weaknesses the Bears offensive line must be prepared to stop Freeney and Mathis because even though the scheme has changed, their mission is still the same: Sack the quarterback.
Matt Eurich is a contributor to Bearsbacker.com. Follow Bears Backer on Facebook and Twitter for up to the minute news about the Bears. Also, check out Matt’s work on Bleacherreport.com and follow him on Twitter @MattEurich.