Generally, a bad run fit can occur for two reasons - they missed the gap or their technique was poor.
As you probably are aware, our defense for the most part (aside from Big Red and the backside 3 Tech, sometimes) will have a single gap to be responsible for during a run play. A gap is exactly how it sounds - the space between two men e.g. between center and guard. Now in junior football, run fits are easy, those gaps never move and guys block straight up.
In the NFL however, with much more pulling and trapping, these gaps can get shuffled around. Now even with all the movement, the number of gaps stays constant (at the first level anyway, once a runner gets to the second level all bets are off). Because the number of gaps stays constant, players should still only be responsible for one but it is much more confusing.
Furthermore, the technique of run fitting can be poor. Generally, in a base defense (not a run blitz) you want all the men to hit the line at the same level because differences in penetration can be exploited by trapping lineman, FBs and are ultimately lanes for RBs. It can create a false second level - and more gaps. For the defensive lineman, this means that they penetrated too far up field (usually when they are about to get trapped) and for linebackers it usually means they cheated by not hitting a player in the gap, allowing him to get to the second level and picking a side.
What has been happening to our young buck LB corps from what I can see is that backside guys are flowing toward the ball carrier, maybe even following trapping blockers, but not filling their backside gap. This can cause defensive lineman to look really bad when it may not be their fault as they are going from playing their own gap to compensating for the LBs mistake by battling across an offensive lineman who already have them hooked. Moreover, frontside guys could be not filling that new gap created by trapping or pulling backside linemen.
Anyway, I haven't studied the defense that closely but those are the general concepts I would use to dissect the running defense in relation to run fits. Ultimately, I think it is a problem with our linebackers rather than our lineman.
ukeface:
