The trendy scheme on defense in 2011 is the 3-4. Coaches have good reason to switch to it too. It adds an extra linebacker, and it takes away a defensive tackle. This puts more speed on the field for the defense, and it allows the defense to bring a fourth rusher from anywhere or not at all. A lot has been made of the possibility of the Jaguars turning to the 3-4, and it would make a lot of sense. Jack Del Rio has said numerous times that they are sticking with a 4-3. Let's take a deeper look at the 3-4.
First, let's touch on what exactly a 3-4 defense is. If you're an avid football follower, you can skip this paragraph, but if you are a casual fan, and you aren't sure what a 3-4 is, read on. A 3-4 defense is a way of saying that there are 3 defensive linemen and 4 linebackers. Thus, 3-4. A 4-3, the other popular base defense has 4 defensive linemen and 3 linebackers. A 3-4 requires linebackers to be very versatile while a 4-3 requires the same of its defensive linemen.
Now that we've covered the basics, let's look at the case for the Jaguars to switch to a 3-4. First and foremost, the Jags have a nose tackle to play in the middle of the defensive line. This would be Terrance Knighton, and he has all the size and ability to play the position. Also, the Jaguars have Alualu to fill one of the starting DE spots. Outside of those two, the Jaguars don't have any defensive linemen that are 3-4 ready.
The linebackers in a 3-4 defense must be versatile, and the Jaguars have a couple of them that could make the transition. Justin Durant (if he's still here) would make a good transition. He would, however, have to get better in his pass coverage. Aaron Kampman would have to move to OLB, and he could do it, but he would lose productivity by moving positions. Daryl Smith would be great for a 3-4 defense. He moves well in coverage, and he's proficient in rush support.
I think it's important to cover the reasons against making the switch. So, here we go. The Jaguars have much of their defensive line already set for a 4-3 defense. Knighton, Alualu, Mincey, and Kampman all fit into their roles pretty well. The Jaguars need some new talent at DE, and I'm sure that will be addressed in the off-season. D'Anthony Smith should be able to add some depth on the defensive line too. Also, to be fair to the 3-4 argument, Smith could be a 3-4 DE, but we don't know how good he is just yet.
The Jaguars linebackers are 4-3 guys. This is the system they've played for a long time, and that type of transition isn't easy to make. I seem to remember Ray Lewis talking about how confusing the 3-4 defense is just after the Ravens make the switch.
The 3-4 does make sense in today's game. This is a pass happy league, and a 3-4 puts more speed and versatility on the field. The fact of the matter is that the running game just isn't as important as it used to be for most teams. I think it's very possible to have a successful 4-3 defense, but you need exceptional players to do it.
Jack Del Rio remains committed to a 4-3 defense, and it's for good reason. The Jaguars would need time to build a solid 3-4 defense, and that's time that Jack Del Rio may not have.