There is a reason why defenses don't utilize this scheme a majority of the time. It puts an emphasis on pressuring the quarterback, but tends to ignore the run game. In short, offenses can exploit this scheme by committing to the ground game.
Smart Football had an interesting take on exactly how offenses can exploit the wide nine:
...This technique...obviously opens up all kinds of issues in the run game: the defensive end aligns so wide the interior offensive linemen can quickly get up to the second level defenders like the linebackers, and the defensive ends are easy marks for traps, draws and counter plays as they sprint upfield.
Here is a prime example of giving a running back too much green field, which happens all too often in this scheme. Adrian Peterson might look like he is flying through the hole, but in all honesty you could drive a bus through that lane.
It remains to be seen just how much teams, including the Detroit Lions, will continue using this scheme with the advent of the pistol offense at this level.
Just on the surface, defensive ends who get up the field would leave a ton of open areas for either the quarterback or the running back to go through on the ground. In addition, asking a linebacker to cover this new formation might be an unenviable task for said linebacker.
Just ask Erik Walden (via Niners Nation).
