A lot has been made about the Cowboys' switch from the 3-4 defense to Monte Kiffin's 4-3, and rightfully so. Although a great defense ultimately comes down to talented players executing a well-crafted scheme, it's not as if elite players can simply line up at any position and succeed. If the chances of success at a particular position are optimized at a certain height, weight and speed, it follows that getting farther from those ideal traits will lower the probability of succeeding.
Kiffin's defenses have typically emphasized speed over size at most positions, and that's certainly a plus for a Cowboys defense that seems as if it hasn't kept up with the NFL's pass-happy evolution. Still, the truth is that the best defensive coordinators tailor their scheme around their personnel.
Kiffin's version of the 4-3 in particular, known as a 4-3 Under, could potentially accommodate the Cowboys' personnel better than most other 4-3 schemes. One reason is the presence of the 1-technique defensive tackle. A 1-technique tackle shades the offensive center, nearly playing heads-up over the top of him like a 3-4 nose tackle. The other defensive tackle, the 3-technique, is typically a smaller player that almost acts as a large defensive end in the interior.
There are certainly areas where the Cowboys might have holes to fill, of course. To figure out just how far away Dallas might be from Kiffin's "dream" defense, I researched the height and weight of each defensive player for Tampa Bay from 2003 to 2008. Kiffin was the defensive coordinator for the Buccaneers during that stretch, emphasizing specific traits at each position. Below are the averages of each player on the roster at every position.
1-DT: 6'3'' 304 pounds
As mentioned, the 1-technique tackle is a strong presence in the inside, but he also has to be nimble enough to shoot up field.
Cowboys' fit: Jay Ratliff (6'4'' 303 pounds) matches Kiffin's prototypical player at this position to a tee. The issue is whether or not the Cowboys can afford to continue to pay Ratliff the big bucks. Sean Lissemore (6'3'' 303 pounds) also fits the bill.
3-DT: 6'2'' 285 pounds
The 3-technique defensive tackle is much smaller than the 1-technique. Also note that, at an average of just 6'2'', the 3-technique is shorter than the defensive ends.
Cowboys' fit: This position in particular is difficult to project for the Cowboys. Jason Hatcher could potentially play any position along the defensive line, although at 6'6'' 305 pounds, he's much taller and heavier than the typically short, light tackles Kiffin has used in the past. Tyrone Crawford (6'4'' 285 pounds) will probably play defensive end, but he also could have some versatility.
DE (Strong): 6'3'' 279 pounds
Kiffin has typically used a very large, bulky player to man his strong-side defensive end position.
Cowboys' fit: If there's evidence that the Cowboys could let Anthony Spencer walk, this might be it. At 250 pounds, Spencer doesn't come anywhere near matching the profile of Kiffin's past ends. As mentioned above, Crawford checks in around this size, but his pass-rushing ability is a question.
DE (Weak): 6'3'' 267 pounds
On the weak side, Kiffin's defensive ends have been relatively close to the same size as the typical 3-4 outside linebacker.
Cowboys' fit: DeMarcus Ware will play this position, although even he is listed at only 254 pounds. Ware shouldn't have much of a problem adjusting, however. Alex Albright might need to transition to this position as well at 6'5'' 260 pounds.
MLB: 6'1'' 232 pounds
The "Mike" linebacker in Kiffin's 4-3 defense has to have the ability to turn and run, so it's no surprise that they've averaged only 232 pounds.
Cowboys' fit: At 6'2'', 245 pounds, Sean Lee is a bit oversized compared to the average 4-3 middle linebacker. He'll often be asked to run downfield when tight ends run vertically, but Lee should be up for the challenge.
WLB: 6'1'' 224 pounds
At only 224 pounds, the average "Will" linebacker in Kiffin's defense must have the speed to run sideline-to-sideline.
Cowboys' fit: Like Lee, Carter is "oversized" for the 4-3 at 240 pounds, but it really shouldn't matter. As one of the fastest linebackers in the NFL, Carter won't have a problem transitioning to the 4-3. He could potentially play any of the three linebacker spots, giving the Cowboys plenty of flexibility heading into the draft.
SLB: 6'1'' 235 pounds
As the biggest of Kiffin's linebackers, the "Sam" is still smaller than all but one linebacker the Cowboys had on the roster in 2012, Ernie Sims.
Cowboys' fit: Assuming Carter plays the "Will," the Cowboys may have a hole to fill here (and vice versa if Kiffin uses Carter as the "Sam." If Dan Connor (6'2'' 242 pounds) ends up starting for Kiffin, he'll almost assuredly play this position and Carter will play the weak side.
CB: 6'0'' 193 pounds
Due to Kiffin's emphasis on Cover 2, his cornerbacks don't turn and run in man coverage as much as in other defenses. Playing near the line, they need to be able to press and play the run, meaning they're typically tall, although perhaps not as heavy as many believe.
Cowboys' fit: Although there are questions about how Brandon Carr and Morris Claiborne can transition to Kiffin's scheme, I think they'll be just fine. Carr has great size at 6'0'' 210 pounds, and it isn't as if they'll be in Cover 2 every play. Even at 5'11'' 185 pounds, Claiborne isn't that far off from Kiffin's prototypical cornerbacks over the years.
S: 6'0'' 207 pounds
Since Kiffin generally plays with two-deep alignments and dares offenses to run, his safeties don't need to be excessively big, but rangy.
Cowboys' fit: The Cowboys could have an issue here since starters Gerald Sensabaugh and Barry Church are both at least 212 pounds and don't necessarily excel in deep coverage. Kiffin has made it work with big safeties like John Lynch in the past, however, but the 'Boys still might need to look for a faster safety of the future in this upcoming draft.
We so often hear that teams need to find "their guys" that fit into their particular schemes, and that's true; certain players are tailored to play in specific ways. However, the job of any coordinator is to mold their scheme to fit the skill sets of the current personnel. It's certainly preferable to have a roster full of players built for a particular scheme, but creating that is a whole lot more challenging than slightly altering the scheme to fit the most talented players on the team.
When all is said and done, the success of Kiffin's tenure in Dallas will be determined by how well he can manage this delicate balancing act, acquiring "his" guys while still being flexible with his scheme to accommodate what he already has.