The Colts moved from the 4-3 defense to a 3-4 hybrid last season under Chuck Pagano, a big difference for Indianapolis fans who had gotten used to the 4-man down line that the Colts' Tampa-2 defense used during the Dungy years.
While some fans took the change in stride, the transition has caused confusion among others, especially considering the fact that the Colts used a 4-man front more often than not in 2012 anyway, even if they called it a 3-4 base defense. The confusion has caused some communication issues amongst fans, and now is as good of a time as any to clarify how the defensive line is generally used, especially with players like Ricky Jean-Francois, Aubrayo Franklin, Josh Chapman and Montori Hughes coming into the fold for 2013.
The Colts' defense in 2012 ran a 3-4, which traditionally has three down linemen: a nose tackle and two defensive ends. In the old 4-3, there were two defensive ends and two defensive tackles (a one-tech nose tackle and a three-tech “under” tackle). The 4-3 was generally a one-gap system, which means the down linemen try to shoot their gaps and get to the backfield, while the linebackers react quickly. The linebackers included a WILL, MIKE, and SAM (weak, middle, and strong-side).
Contrarily, the 3-4 defense traditionally is a two-gap system. The two-gap focuses more on the linemen reacting to the blockers. Often, this ends in the linemen (especially the nose tackle) occupying space and controlling multiple offensive linemen, allowing the linebackers more time to react, read the play and make tackles. The linebackers include two very athletic, versatile outside linebackers and WILL and MIKE inside linebackers.
The Colts' hybrid uses a base 3-4 with a two-gap system, but adds in the wrinkle of a consistent rush outside linebacker on the weak side (opposite the tight end) by sliding the defensive line down a gap.
In the Colts’ scheme, the nose tackle sits on the one-gap to the strong-side (usually the center’s right shoulder). The 3-tech defensive end is on the weak-side, on the guard’s outside shoulder. The 5-tech defensive end is on the strong side either directly on the tackle or on his outside shoulder. Meanwhile, the rush outside linebacker (ROLB) slides down in a 9-tech rush spot on the weak side (way outside the tackle, on the outside of where the tight end would be). See the diagram below for example.
The tight end is most commonly used on the right side of the line, so the strong-side linebacker (SOLB) is usually on that side as well, leaving the ROLB across from the left tackle, the same position that RDE edge rushers like Dwight Freeney generally found themselves in in the 4-3.
Here is an example of the Colts in this base 3-4:
And here are the Colts in the scheme when the offense switches the tight end, putting him next to the left tackle. As you can see, the defense slides over to fill the same gaps on the other side.
The nose tackle in this scheme generally is responsible for eating space and occupying both the center and the right guard (or the left guard if the tight end is on the left side). The 3-tech defensive end is usually sealing off the backside of runs, and needs to be able to hold his ground and keep the edge, but is more of a chaser from the backside and gap penetrator in pass rush. The 5-tech defensive end needs to be strong, since he is usually facing the run head-on on the strong side, but he also is often the DL’s strongest pass-rusher opposite the ROLB.
The Colts and some analysts differentiate between the three and five-tech defensive ends by listing 3-tech’s as defensive tackles (although not as nose tackles).
You can see this difference on the Colts roster listed on the team’s website.
Listed as DEs are Cory Redding (the team’s primary 5-tech last season), Fili Moala and Lawrence Guy. Listed as defensive tackles are Drake Nevis (makes sense as the team’s best run defender last season), Ricardo Mathews, Ricky Jean Francois, Montori Hughes and Kellen Heard. Nose tackles listed include Aubrayo Franklin, Josh Chapman, Brandon McKinney and Martin Tevaseu.
So, if you hear guys like Nevis, Mathews, Jean Francois, Heard and (most notably) Hughes referred to as both defensive tackles and defensive ends, you’ll know the reason. While in a traditional 3-4 they qualify as ends, their position can be similar to a 4-3 under-tackle, and they are often classified as such.
I think this was actually a pretty good way to approach this (Wiithout using 10,000 words.) as it seems to me that calling a defense a 4-3 or a 3-4 is really a way of identifying what you are asking your lineman to do. Since in the vast majority of situations, a defense called a 3-4 will have more than 3 players on the line of scrimmage.