Techniques are the foundation of football, and it’s impossible to have a meaningful discussion about schemes and systems without at least a rudimentary understanding of techniques. With regard to defensive fronts, there are two basic families of techniques: 2-gap and 1-gap (both of which are, to some degree, misnomers), which I’ll cover briefly so that we can move on to some of the schemes and systems we might reasonably expect to see from an Odom/Cross defense.
In 2-gap technique, each defensive lineman (DL) and linebacker (LB) lines up directly across from (head-up on) an offensive lineman (OL) or tight end (TE) and could be responsible for either of the 2-gaps on either side of that OL or TE, depending on what that OL or TE does, like so:
In practice, however, the DL and Outside LBs’ (OLBs) job is to attack directly up the centerline of that OL or TE, engage him to prevent him from moving on to block the Inside LBs (ILBs), drive him into the backfield, read his block then fight across it to get into 1 of those 2 gaps. Basically, engage, read, then go wherever the OL doesn’t want you to go, like so:
In this example (an iso play), the TE and RT want to double team the defensive tackle (DT) and drive him back towards the playside ILB before one of them scrapes off to block him, and the same for the RG and C against nose tackle (NT) and backside ILB. However, it’s the responsibility of the OLB to engage the TE so that he can’t double team the DT, and the responsibility of the DT and NT to hold their ground against the double teams, leaving the ILBs free to make the tackle.
An advantage of 2-gap technique is that by engaging and reading the OL, the defense can reliably smother almost any run play without being caught out of position. A disadvantage is that in order to fill a 2-deep roster, a team needs 6 DLs who can reliably move a single OL into the backfield or hold their ground against a doubleteam and 4 OLBs who can reliably drive a TE into the backfield against the run or cover him man-to-man against the pass. Due to this, only teams that can reliably recruit at an extremely high level play a base 2-gap technique.
In 1-gap technique, each DL and LB lines up on the outside shoulder (shaded) on an OL or TE, and is responsible for occupying the gap in which they’re aligned, like so:
In most variations of the 1-gap, the DLs are responsible for attacking the shoulder of the OL or TE on which they’re aligned, to prevent them from moving on to the block the LBs and squeeze the opposite gap for which the LB is responsible, but also for penetrating into the backfield to disrupt plays and make tackles.
An advantage of a 1-gap technique are that it can be played by a wider variety of players; from the same types of players who engage the OL and protect linebackers in a 2-gap system to smaller, faster players who penetrate and disrupt. A disadvantage is that by penetrating into the backfield, DLs and LBs can be vulnerable to be read (as on option plays) or being lead blocked by fullbacks (FBs) and h-backs (HBs) or trap blocked by pulling OLs.
Now that we’ve touched briefly on technique, we can talk about Fronts, or how those individual techniques come together to form a coherent run defense. While spread offenses have forced most teams into a 5-defensive back (DB) defense on most downs, there are still two basic families of scheme: 3-4 (indicating 3 DLs and 4 LBs) and 4-3 (however, due hybrid players that assume some of the roles and responsibilities or both a DL and LB, these are, again, to some degree, misnomers). An advantage of the 3-4 is that the defense can disguise where the 4th pass rusher is coming from, giving the 3-4 greater versatility. The advantage of the 4-3 is that because the 4 DLs are almost always the 4 pass rushers, they can specialize and excel in their rolls.
The 3-4 Family
The 2-Gap 3-4
In the beginning, there was the 2-gap 3-4.
Descended from the older 5-2, the 3-4 replaced the defensive ends (DEs) in a 3-point stance with stand-up OLBs at the line of scrimmage (LOS) who assume some of the roles of both DEs and OLBs. With 3 head-up DLs and 2 OLBs on the LOS, the 3-4 leaves only the guards uncovered, and hopes to pin both of them at the LOS by demanding double teams on the DLs, leaving the ILBs free to make tackles.
The 1-Gap 3-4
But as mentioned earlier, there are relatively few teams that can reliably field a base 2-gap 3-4. Because of this, many 3-4 teams have moved to a 1-gap variation. We can visualize this evolution first by imagining a 2-gap 3-4 team predetermining which gap they’ll occupy (in this case, the strong side of the formation), then sliding over to be shaded on the outside shoulder of OL or TE to the inside of that gap, like so:
The 4-3 Family
The 1-Gap 4-3 Over
When most people talk about the 4-3, what they’re really talking about is the 4-3 Over. In the Over, the defense slides to the strong side of the formation, and shades on the outside shoulder of the OL or TE to the inside of that gap, as we previous discussed for the 1-Gap 3-4.
The 1-Gap 4-3 Under
To cover up an additional OL and provide additional strength against the run, many 4-3 teams will shift into the Under front. In the Under, the DLs slide to the weak side of the formation, with the strongside (Sam) linebacker walking up to the LOS, like so:
Now, if we compare the 1-gap 3-4 and 4-3 Under above, we can see an example of convergent evolution. In practice, the differences are even smaller than they appear on paper: the 3-4 DT and 4-3 DE in the outside shade on the strongside tackle would be of very similar body types and have identical responsibilities, as would the 3-4 OLB and 4-3 DE in an outside shade on the weakside tackle.
These differences become even smaller when any of the 1-gap defenses shifts into the nickel, substituting an additional defensive back, the nickel back (NB), for the Sam, like so:
As you can see, the only difference between the Over and the Under is the shift of the interior DLs, as there’s no longer a Sam linebacker to be on the LOS or provide the threat of a 4th pass rusher. Consequently, the weakside OLB in the 3-4 is almost certainly the 4th pass rusher, skewing his roll even further towards that of a DE and further from an OLB.
Based on what we saw of Barry Odom at Memphis and his one year as DC at Mizzou, it’s not unreasonable to assume this 1-gap, 3-4/4-3 hybrid is exactly the sort of hybrid defense he would like to run, and Charles Harris provides exactly the sort of hybrid LB/DE athlete who could make it work.
As I mentioned, spread offenses have forced most teams in to 5-DB defenses on most downs, but the defense must still account for the possibility of the run, particularly against "power" spread teams such as those run by Urban Meyer, Dan Mullen, and Gus Malzahn, that make extensive use of big TEs and HBs as both lead blockers and pass-catching threats. To counter these types of players, defenses have increasing utilized hybrid LB/DB players, who are capable of both engaging TEs and HBs in run support like a LB or covering them in pass defense like a DB. It’s this type of player that Gary Patterson (and consequently Cross) employed at strong safety ($) at TCU, like so:
(Note that in Patterson’s defense, in contrast to more conventional defenses, the $ replaces the NB, the free safety (FS) replaces the $, and the weak safety (WS) replaces the FS.)
Another wrinkle that Patterson introduced is divorcing the defensive front and backfield calls, thus creating a "modular" defense where the front could match the offensive front and backfield, while the defensive backfield could match the receivers, without creating any weak points between the front and backfield. (This is also the source of Cross’ "co-DC" title at TCU, as Patterson has different coaches calling the front and coverage.) Others have already covered this in some detail, so I won’t cover it here, but just as it’s the hybrid DE/LB that makes the hybrid 3-4/4-3 work; it’s the hybrid LB/DB that makes this 4-3/4-2 hybrid work.
Mizzou has traditionally been an even coverage team, and in modern football, that means a Cover 4, or Quarters. Unlike Cover 0 through Cover 3, which strictly indicate the number of defensive backs dropping deep, Cover 4 is a Cover 2 that has the ability to morph into quarter/quarter/half or Cover 4 against multiple vertical threats. The simplest way to think of it is as Cover 2, with the following exceptions:
The corners read the release of the widest receiver on each side. If he goes deep, they run with him as in man (the biggest single difference from Cover 2, where they’d do their best to jam/redirect him, then drop him and let the safety pick him up), otherwise they’ll play regular Cover 2 rules.
The safeties read the release of the 2nd widest receiver on each side. If he goes deep, they run with him as in man, otherwise they continue to stay deeper than the deepest man and play Cover 2 rules.
In both cases, the three LBs (or, in this case, the LBs and the $) play underneath zone and are not only responsible for covering any receivers running short routes, but for jamming/redirecting any receivers releasing deep so that they can’t run straight up the seams between the DBs dropping deep.
So against multiple short routes, as one might see in a West Coast offense, Cover 4 looks like a conventional Cover 2 over 5, with 5 underneath defenders to swarm short routes, but against 4 verts (the bane of traditional Cover 2 and 3,) it morphs into Cover 4 over 3, with 4 DBs basically playing man against the 4 vertical threats, with 3 underneath defenders left to deal with backs sneaking out of the backfield.
The major exception is vs. trips, where the third receiver outnumbers the 2 potential deep DBs to that side. In that case, the $ slides out over the #2 receiver, with the FS taking the #3, but the some basic principles apply, meaning that if all 3 receivers go deep, the $ must be competent enough to cover the #2 receiver 1-on-1.
Putting It All Together
It doesn’t take a great deal of imagination to put both concepts together, and in fact, some already have. In practice, it would look something like this, with 3 "true" DLs, 1 DL/LB hybrid to the weak side, 2 "true" LBs, 1 LB/DB hybrid to the strong side, and 4 "true" DBs:
And to bring it full circle, there’s no reason that against an attached TE, the $ couldn’t walk up to the LOS, like so:
Further, Odom has shown a willingness to bring his DBs as pass rushers, bringing back the threat of a 4th pass rusher coming from an unexpected spot on the field.