First, a quick recap of the obvious: we run a 4-3 defense, specifically of the Jim Johnson variety. This means that the responsibilities of the defensive line, especially in the run game, are far more geared to eating up blocks and containing their gaps than tackling the ballcarrier. That responsibility lies with the linebackers, who should have clear lanes left for them if the DTs are doing their jobs.
And guess what, they often were. The Chicago game stands out to me in particular; almost all of Forte's best runs came either off tackle (the DE and safety's responsibility) or through a hole that a linebacker had just shot through and completely whiffed in the backfield.
For example, take this offset I formation:
The fullback is lined up on the strong side, and James Anderson is showing a weakside blitz.
Here's the view from the coaches film, showing our 4-3 formation with Charles Johnson lined up strong side and Hardy on the weak:
At the snap, you see James take off on his blitz, Charles Johnson gets doubled by the tight end at right tackle, Fua does his job and takes up two blocks and slows down the right guard, McClain gets such a nice burst that the left guard has no choice but to chop block him, and Hardy fights to contain the cutback lane. Notice the arrow indicating Jason Williams free pass into the backfield, which is the entire point of running an aggressive Jim Johnson 4-3: giving your linebackers the opportunity to take down the ball carrier unblocked.
Unfortunately, Williams is not up to the task: he overshoots Forte completely, and Sherrod Martin gets completely turned around on his block and fails to prevent Forte from getting to the next level.
The play resulted in a 46 yard gash, with Charles Godfrey completely whiffing on a tackle that would have held the gain to half that, and Captain Munnerlyn and Darius Butler have to save the day with a tackle from behind (interestingly enough, McClain has an excellent chance to catch him from behind as well. He shows some surprising feet for a DT!) All of this happened even though the defensive tackles and ends all did their jobs adequately, and gave a linebacker a direct path into the backfield to tackle the ballcarrier.
This is a theme throughout the season, where even when the DTs made a nice push on the pocket or ate up the blocks necessary to give the linebackers the chance to clean up, almost no one but James Anderson was really up to the task, as Conner and Senn repeatedly failed to shed blocks or make tackles within their lanes. Even worse, once the ballcarriers got past the linebackers, they often made mincemeat of both Martin and Godfrey. This is not to say our DT corps could not stand improvement, because it absolutely could, especially since the line play improved when the rookies sat down and the more experienced DTs like Neblett and
In this context, the absence of a DT pick in our draft and the #9 selection of tackling monster Luke Kuechly makes perfect sense.