The Dallas Cowboys could be switching defensive schemes after hiring Monte Kiffin to replace Rob Ryan as defensive coordinator.'s Gregg Rosenthal confirmed Kiffin's appointment and expects a switch to a 4-3 defense. That presents some challenges to the existing 3-4 personnel.

When examining how Kiffin's defense might look in Dallas, it is important to start with the 'under' front. Kiffin ran that system with the Minnesota Vikings and later used it to dominate the league with the Tampa Bay Buccaneers. It is a 4-3 look, with some 3-4 crossover.

The four defensive linemen are shifted to the open side of an offense, away from a tight end. The weak-side end aligns just outside the left offensive tackle and is the scheme's primary pass-rusher.

That position is ideal for DeMarcus Ware. The cat-quick pressure specialist is the most prolific pass-rusher of his generation. If switching to Kiffin's scheme has one major advantage, it's that it will create more rush opportunities for Ware.

Next to him will be the under-tackle. This is an interior lineman, aligned in the weak-side B-gap, between the left tackle and left guard. Along with the rush end, the under-tackle should have a one-on-one rush opportunity on most plays. That could prove very useful for a player like Jay Ratliff. While a dominant 3-4 nose tackle in his own right, Ratliff lacks prototype size for the position.

Instead, he has relied on quickly spiltting gaps to attack the backfield with speed and technique. He could return to his dominant best in a more attack-minded role. In Tampa Bay, Kiffin's rush end, under-tackle combination was Simeon Rice and prospective Hall of Famer Warren Sapp. That dominant duo wrecked multiple offensive gameplans and blocking schemes. A tandem of Ware and Ratliff offers similar potential.

The position of these two linemen is also key because of how they protect the weak-side linebacker. Possibly the most demanding position in Kiffin's schemes, the Will linebacker aligns behind the rush end and under-tackle.

He is usually a lighter, more athletic linebacker, blessed with excellent instincts and elite sideline-to-sideline speed. Think back to Buccaneers great Derrick Brooks, as the prototype for this position. The Cowboys already have a player in a similar mould. Youngster Bruce Carter certainly has the range and quickness to fill this key role, provided he can stay healthy.

Next to him, the middle linebacker position is also vital, but in a different way. Kiffin became famous for how he matched the 'under' front with the Tampa-2 coverage scheme. It is based on a two-deep shell, with both safeties covering the deep halves of the field. What the Tampa-2 concept adds is the presence of the middle linebacker, who drops back to cover the gap between the two safeties.

This limits the offense to short throws underneath, where the speedy outside linebackers are expected to make instant tackles. Intelligent and ultra-athletic playmaker Sean Lee is a perfect fit for this position.

Like Carter, Lee has injury concerns. However, when healthy, he is the Cowboys' most skilled defensive player. He could man the middle of Kiffin's system in the same way Brian Urlacher has for the Chicago Bears, under Kiffin disciple, Lovie Smith.

Those are some of the pieces Kiffin has and how his schemes can make them effective. What he doesn't have is a powerful presence in the middle.

The focal point of the 'under' front's run defense is a big-bodied nose tackle. This nose tackle lines up in a shaded technique, just to the side of the center, rather than directly over him, as in a 3-4. However, similar to a 3-4, the 'under' front nose tackle must occupy double teams. This creates those enticing rush opportunities for the rush end and under-tackle.

The Cowboys don't really possess that player. That's especially true if Ratliff is moved off the center. Jason Hatcher is more of a gap pentrator, rather than an immovable force in the middle.

Kiffin also doesn't have a savvy safety to act as the leader of his disciplined coverage schemes. In Tampa Bay he had John Lynch and will need to acquire a defensive back in a similar mould.

However, Kiffin can make the cornerback tandem of Brandon Carr and Morris Claiborne better. The coverage will have more of a structure and be less risky than it was under the often reckless Ryan.

That's not to say Kiffin won't attack. He is particularly fond of the cornerback blitz and Ronder Barber became the league's all-time sack leader among corners, while working for Kiffin.

Bringing the 72-year-old Kiffin back to the NFL is a gamble and switching schemes is equally risky. The Cowboys have invested a lot in 3-4 personnel. However, the results simply haven't matched that investment. They ranked 24th in points allowed this season and couldn't protect a lead in 2011.

If they are going to switch to a 4-3, then the 'under' front is the safest choice. Kiffin can tweak his players to fit a simple, effective and proven framework. Having him run the defense will mean excellent coaching without the drama and distractions Ryan's brash antics often inspired.

Kiffin is a true master of defense and by naming him coordinator, the Cowboys may have already made their smartest move of the offseason.

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