The Cardinals moved to a 3-4 base defense when Ken Whisenhunt took over as coach in 2007, but they have yet to gather the type of personnel they need to operate it effectively.
Whisenhunt has envisioned a defensive scheme in the mold of his former team, the Steelers. He figured he needed a stout nose tackle and versatile linebackers, including those who could effectively rush off the edge.
But the Cardinals have yet to find the right fits in either the draft or free agency. And it's limited them severely on that side of the ball.
In 2007, they moved up in the draft to take nose tackle Alan Branch. But he turned out to be a far better end than nose tackle.
Last year, they took Dan Williams in the first round. While Williams has improved, he did not make an impact during the first three quarters of the season.
The Cardinals are hoping he turns into a Casey Hampton type of player, but that's questionable at this point.
They have also failed to acquire impact outside linebackers. Cody Brown, a second-round pick in 2009, flopped and was cut last year. Will Davis showed some promise but is out for the year with injury.
Joey Porter, signed this offseason in free agency, has shown signs of age and has only five sacks, despite playing in all passing situations this year.
The only promising pass rushing linebacker is O'Brien Schofield, who missed half the season with a knee injury.
The secondary has taken criticism all season, but it would be much more effective if the Cardinals could bring consistent pressure. As much as this team needs to address its quarterback situation, finding an elite pass rusher is almost as important.
In the loss to the Panthers last week, the Cardinals used the 4-3 about half the team, especially early on run downs. That's mostly because the Panthers can't pass the ball, and the Cardinals focus was on stopping the run.