Not known for their athletic ability, this unit's strength is in their flexibility and intelligence. Mike Vrabel and Adalius Thomas can play any of the four linebacker positions in this defense. Tedy Bruschi can play either inside position and Rosevelt Colvin can play either outside position. Bruschi and Vrabel have been in this system since the turn of the century, Colvin since 2003, and Thomas was added in the offseason, but all are extremely intelligent, know the system well and can adapt the play call to suit a given situation.
All told, they have 13 sacks, 8 forced fumbles and two interceptions. Vrabel accounts for eight of those sacks and five of the forced fumbles, accumulating three of each against Washington last week, and has been more deadly rushing the passer than covering passes so far this season. He has lined up on the strong side, the weak side, and the middle of the defense at different points and has come on the blitz from all locations. The key for Manning and the Colts will be to make sure they are cognizant of where he lines up on every play. Joseph Addai and Kenton Keith are solid in pass protection and should be able to contain Vrabel long enough for Manning to get rid of the ball.
Facing such a malleable defense, it would most likely be a prudent move to adopt a zone-blocking scheme in the passing game. Against the Redskins in particular, this would have been effective since the Patriots linebackers seem to take full advantage of the "outside-inside" approach that most offensive linemen take in a blitz situation. On two of his sack/forced fumble plays, Vrabel lined up on the weak side and the defensive lineman started outside, then swam to the inside at the snap. In both situations, the right tackle went to engage the lineman first, not turning his head to block the blitzing Vrabel until it was too late.
Indianapolis has been susceptible to this strategy in the past, so it's critical that they do not fall for it on Sunday.
In the running game, life actually gets a little easier for the Colts. Neither Vrabel nor Colvin have the speed to get to catch Addai when he runs the ball outside the tackles. However, since the focus of the running game will need to be between the tackles, the best idea will be to take advantage of the recognition skills of the linebackers by running counter plays that start inside but bounce to the outside.
This will need to be worked into the offense slowly as the game progresses depending on how well the inside running game is doing. If Indianapolis has early success running between the tackles -- hopefully by forcing Wilfork to remove himself from the play and getting Lilja and Scott isolated on Bruschi and Thomas -- that will, of course, open up the play-action passing game, but make the counter plays that much more deadly.