The 3-4 defense is chic again in the NFL; it's all the rage. The Packers and Broncos both are reportedly switching to the 3-4 this offseason. The majority of the best defenses right now are running the 3-4: Pittsburgh, Baltimore, New England, San Diego.
So why not join them? Well, it's not that simple; you have to have the proper personnel to change.
On the surface, It seems really easy—just subtract a down lineman and add a linebacker, right?
Wrong. The size of almost everyone on the front seven has to be bigger. The DTs that generally weigh around 300 lbs. in a 4-3 now have to weigh closer to 330 because they now have to take on two linemen. The DEs now have to weigh upwards of 300 lbs.
Even the LBs have to be bigger and stronger, because they now have to take on more offensive linemen.
Just as a reference:
Chris Canty - 6'7, 305
Marcus Spears - 6'4 305
Aaron Smith - 6'5 300
Brett Keisel - 6'5 285
New England DEs:
Richard Seymour - 6'6 310
Ty Warren - 6'5 300
Glenn Dorsey - 6'1 300
Doesn't really fit, huh?
Don't get me wrong, though, if the Chiefs switched to a 3-4 tomorrow, Dorsey would have to play DE, and would do OK. But the Chiefs are paying him $51 million to get in the backfield and be a one-gap, disruptive force, not a two-gap run-stuffer that simply takes on blockers. That's just not the kind of player he is.
Dorsey finding a spot to play is only half of the problem; finding LBs to play in the system is the other. As is, the Chiefs have exactly one starting LB worthy in the 3-4. Derrick Johnson could move inside and play one of the ILB spots.
The other three spots would have to be filled. Finding the other ILB would not be too hard, most LBs can play in that spot. It's finding the guys who can play on the outside that is really hard.
The OLBs in a 3-4 have to be big (6'2+), strong (260+ lbs.), and fast. Shawne Merriman is a perfect example—he is 6'4, 270 lbs. People who are 260 lbs. and super-athletic are just a rare breed. They are few and far between, like true NTs. The Chiefs have none of these guys on the roster and would have to work hard to find some suitable before the season started.
The best, and smartest, thing for the Chiefs to do is take it slow and acquire 3-4 talent when they can. Do what the Cardinals did this past year and mix in a few 3-4 looks during a game. Be deliberate and make the switch when it is best for the football team.