Five reasons Colts D will struggle

Dwight Freeney has ben terrific as an end in the 4-3, but he could struggle in the Colts' new scheme. Doug Benc/Getty Images

The Andrew Luck era has begun in Indianapolis. But not only are the Colts rebuilding their offense, the defense is undergoing a facelift as well.

The 4-3, Cover-2 defense that was so well known throughout the Peyton Manning era is a thing of the past, replaced by new coach Chuck Pagano's 3-4 system. While a massive scheme transition on defense usually takes a while to lean, the Colts are in additional trouble because their personnel simply doesn't match up with the new system.

Here are five reasons the Colts defense will struggle moving to the 3-4:

Dwight Freeney and Robert Mathis switching to 3-4 OLBs

Freeney and Mathis have played at a very high level for their entire careers as 4-3 defensive ends with their hand on the dirt (or turf). In Pagano's 3-4 defense, while they will still be asked to provide pass-rush pressure, the duo will have to drop into coverage occasionally as well. Neither has spent significant time in the up position, nor have they had any significant experience in coverage.