[caption id="attachment_12032" align="alignleft" width="215" caption="Antonio "Mookie" Johnson tackles Titans running back Chris Johnson. (Andy Lyons | Getty Images)"][/caption] The Indianapolis Colts have historically had difficulty putting together a group of defensive tackles that are capable of fulfilling their responsibilities in the Tampa-2 defensive scheme. In this scheme, the nose tackle -- 1-technique tackle -- is asked to be a space-filling, line holding run stuffer. The under tackle -- 3-technique tackle -- is asked to penetrate the offensive line to disrupt running lanes on the way to the quarterback. For many years the biggest weakness amongst Indy's interior defensive linemen has been a lack of size. This resulted in opponents running the ball relentlessly off of their centers and guards, right through the middle of the Colts defensive line. A lot has changed. Now Antonio Johnson, Daniel Muir, and Fili Moala all surpass the 300-pound mark. Only Johnson is well-suited to play nose tackle, while Muir and Moala are reasonably sized 3-technique tackles in a 4-3 defensive front -- Muir had great success in 2009 and Moala showed marked improvement in 2010. Ricardo Mathews and Eric Foster are used situationally on passing downs and are better suited for the under tackle role. Foster moves outside to defensive end in run packages -- Mathews may do the same in 2011. Some fans attributed much of the Colts struggles defending the run to the defensive tackles. To be sure, when Muir had to start out of position, the interior was not as stout as it would be with Johnson, but even then most of the problems are more directly related to difficulties with the Colts defensive scheme and gap discipline breakdowns amongst the linebackers. The reality is, if the Colts are able to retain Johnson, Muir, and Foster for 2011, the position needs very little to be successful. Antonio Johnson has to be the highest priority free agent defensive tackle during the off-season as without him the team will be forced to rely on the draft or free agency to fill the nose tackle role. Traditionally, rookie defensive linemen take a year to get acclimated to NFL offensive linemen, which means Indianapolis would be conceding to taking a likely step back at the position in the coming season. Muir was a whipping boy amongst fans in 2010 because he struggled in the space filling, line holding nose tackle role. Such criticism should not dominate fans minds as free agency approaches because only Muir is proven depth at under tackle during primary downs. If Muir is not retained the team will have to rely on Mathews developing into his rotational role. This could save the team some money and may work out, so if the decision is made to let Muir go, fans should not misunderstand it as an indictment of his abilities as a 1-technique tackle. It will be made because the front office is comfortable with Mathews filling the backup role to Moala. Another defensive tackle who stepped up his productivity in 2010 was Eric Foster. Foster improved as an interior pass rusher, forcing quarterbacks out of the pocket, allowing Dwight Freeney and Robert Mathis to wreak havoc. Such a player is valuable to the Colts, even if he is used only situationally. Additionally, the fact that he has experience playing as one of the team's starting defensive tackles in previous years makes him valuable as a run down and short yardage defensive end. Look for the team to make an effort to re-sign him. Finding a player with his talents and flexibility is not easy. If Foster and Johnson are retained, the Colts will only need to look for another run stuffer through the draft or free agency. If Muir is retained that need drops enough to allow the team to look only to the later rounds for a potential project player -- or for an unproven second-year free agent. One free agent the team should take a close look at is Brandon Mebane, who will be entering free agency as his rookie contract is expiring in Seattle. Mebane is not only capable of stopping the run, he also is strong enough to get to the quarterback. As Mebane is not a big enough name in the NFL to demand a cap debilitating contract, there is a chance the team could pick him up and bolster the defensive line significantly for 2011. Such a move would likely only occur if Muir is not retained. As odd as it sounds, defensive tackle is one of the strongest units for the Colts franchise for the first time since Booger McFarland was on the team in 2006. With Moala and Mathews gaining experience, and a couple of key re-signings, Indianapolis should be in fine shape at defensive tackle. Bill Polian has done a magnificent job bringing the position along after it neared epidemic proportions with the undersized Keyunta Dawson and Eric Foster starting in 2008.