Minnesota’s run defense played pretty well against Northwestern. Mostly utilizing Cover 4, they were able to maintain numbers advantage inside the box for most of the game. When they did get gashed though, it was mostly because the backside was slow in pursuit. In Cover 4, the LBs, particularly the backside LB, must flow fast. If he reads the play immediately, he can tend to read “cloudy/clear” and shoot off the butt of a pulling OL or beat a zone blocking OL across his face and blow up the play in the backfield. If he can’t do that, he must scrape over the top quickly to get to the playside.
Backside LB Slow in Pursuit
Why is it so important for the backside LB to flow fast? Because in cover 4, the backside safety will typically maintain backsidecutback responsibility. He must work down to the LB level and tackle any cut back that comes his direction. When the backside LB doesn’t flow fast, a crease forms between the frontside LBs and the backside. We’ll take a look at it here.
Here’s the man to keep an eye on.
Immediately after the snap, you see the frontside LBs flowing fast outside, looking to meet the RB at the point of attack, chasing from inside-out. Likewise, the frontside safety has alley fill responsibility, so he will force everything back inside to the fast flowing frontside LBs. But the backside LB is slow to read the play.
You see here that he has hardly moved and the RB has been given the ball.
Once he reads the play, he still isn’t fast flowing, but instead is not confident in his read and you start to see the crease forming.
By the time the backside OL gets into their blocks, you see this. The LB has been sealed behind the DE and can’t cut down the lane. There are three defenders in the same, outside gap now, and no one to prevent this vertical cut.
That leads to a big play, which can be seen here.
Fast Pursuit from Backside LB
Here’s why you need fast pursuit from the backside LB.
At the snap of the ball the LB is already crashing, and his eyes go to the backfield to the OL as he begins reading “clear/cloudy”.
By the time the RB cuts vertical, the OL cannot get into the LB and reach him, and his pursuit takes him right to the ball carrier.
Here’s the video.
Everyone Else Must Do Their Job
One of the primary things with Cover 4 is that everyone must do their job for all gaps to be accounted for. The backside LB has won his helmet across playside. Here, Northwestern again cuts it back. This is a nob adjustment, so the CB to the bottom of the screen has cloud leverage. But note how the CB has failed to squeeze down the backside gap and stays way too far outside.
Luckily for Minnesota, the backside LB is able to fight back across to the ball carrier and prevent this from going longer. Here's the video.
The same can be said for the safety position. They must do their job as well. And when everyone did, Minnesota shut down the Northwestern run game. But when someone failed to do their job, either a LB fast flowing, a safety coming down to the LB level on the backside quick enough, or the CB squeezing the backside cutback, all defenders must do their assignment to the Cover 4 defense to be gap sound.