There is a reason so many spread teams are using 2o personnel as a base formation. Slot-T teams like Auburn use jet motion and pulling guards to out leverage the defense, even using RPOs to find wide open receivers downfield. Florida St. uses a split-backfield to 
attack the defense with speed to the edge. Teams like Baylor and Ole Miss use 20 pers. formations to use RPO style attacks, Baylor with the third level vertical option routes and Ole Miss with Arc-Read RPOs. There are multiple ways to attack a defense from 20 pers. just using the backfields alone. Each set can create a different read for the QB (all this without using unbalanced and motion). The diagram to the left depicts some of the more popular backfields an offense likes to run out of 20 pers (this doesn’t even include Pistol or “I” sets). When breaking down a 20 pers. offense, each backfield creates a new formation. If an offense uses each one of the above backfield sets in their offense, it forces the defense to look at the formational data with a more critical eye.
For a defensive coach, 20 pers. causes problems not only in the backfield but with the three receivers. There is a tendency by some DC’s to spin against 20 pers. The thought process behind spinning is the offense has added another blocker, and potentially another gap, so to counteract t
hat, a DC will spin. The diagram to the right depicts a defense that has spun to the H-back. This allows the Sam to work back to the box. Though the defense has created a plus-one to the field, they have left themselves exposed to the boundary. All an offense has to do is run a simple Arc-Read to the boundary and the offense has a numbers advantage. If a defense is going to spin against 20 pers., it is in the defense’s best interest to spin weak. Leveraging the boundary allows the pass distribution to the field stay intact, and a defense can play a hybrid quarters scheme to the boundary. The issue with spinning to the boundary is the third-level RPO read off the dropping safety. Teams that run a backside choice with the single receiver will see the dropping safety and run a post/slant right behind him. The best plan of action versus a 20 pers. offense is to stay in a two-high scheme and use the safeties as extra box players. The question now is, what about the front?
The Over Front
The Over Front is great against teams that run a more traditional run game (Power/Counter). As seen in the diagram above, the Mike and Will are the box players. This allows the Sam to cover down and the DS to the boundary is the “O” gap fitter. If a DC is afraid of the X-Hitch to the boundary he can press the WR and still play a Four-Read scheme (DS aggressive to fit) or a Two-Read scheme that puts the CB as the force player on the edge. Many times, spread teams will tempo their power run game. Running an Over Front allows the Mike to easily identify the H-back and set the front his way. As stated earlier, the secondary can play with the coverages depending on down and distance and tendency.
Below is a depiction of a traditional run game tagged with a backside RPO. The quarterback is reading the leverage of the CB. If the CB gets too far off the WR the QB will throw the hitch. As offenses become more advanced in their RPO schemes, the QB can read the leverage of the DS and throw a slant or post.
In this particular play, the DE to the field will get kicked out by the H-back. The DE’s main responsibility is to step down with the down blocking OT. As the H-back approaches, the DE will set the edge and force the play back inside (versus gun/spread the rule is for the DEs to be the force players). The Mike’s responsibility is to hit the outside shoulder of the pulling guard. If the play bounces (or the DE happens to wrong-arm the fit), he scrapes to make the tackle. The Will steps to his gap and sees the puller. His fit is the inside shoulder of the pulling guard. The Tackle has to challenge the double-team and hopefully create a situation where the OT can’t sift up to the Will (if the OT gets to the Will, he will scrape to the puller). The Nose crosses the face of the block back to create a plus-one to the play side. In the secondary, the DS fits into the cutback lane and corrects the Will if he gets pinned, or scrapes too high and the RB has a cutback lane.I always teach my boundary CB against a single WR to treat it like man unless I’ve called a particular coverage check.
The key in any front is to allow the box players to stay in the box fit and read their keys. The DEs in against the spread have to be the force players in order to combat the many ways an offense can use a stretch path to trick the eyes of the ILBs. In the diagram to the left, the offense runs a QB Counter but uses the stretch path by the RB to get the LBs to freeze. If taught right, the LBs will read their keys and fit the counter play. The numbers are plused each way. In this particular play, the DE to the counter side boxes and makes the H-back work outside. This gives the LBs time to fit the pull of the H-back (and the DS is there as clean-up). If the QB would have handed the ball off to the RB, the DE to the field will attack upfield because the three technique is in the gap next to him. In the secondary, the Sam will cross-face on the slots block and the CS will correct the fit. The key, as stated above, is to stay even and keep the box’s integrity.
Note :: I always teach my boundary CB against a single WR to treat it like man unless I’ve called a different coverage to counteract an RPO or a certain route. In the example above, I am running Sky coverage to allow the DS to play like a “Robber” and fit into the cutback/curl.
The Under Front
Defenses turn to an Under Front when an offense uses quick motion (Jet) and tries to run outside to the field. Setting the three technique away from the H-back allows the Mike to widen his alignment and be quick to read flow outside. Offenses that like to run unbalanced sets and Jet Motion to out leverage the defense can be combated with an Under Front. In the diagram above, the fits do not change for an Over Front, they just shift away from the H-back. If there is a clear tendency to run outside, the Mike can align in a 40 and stack the OT.
In the diagram below, the offense is running an Arc-Read (Bubble) play. The Under Front forces the QB to pull the ball because the DE to the field has the dive (lack of anchor in the “B” gap with a Nose). The Sam is able to cover down because he does not have a gap in the run fit. The cover down forces the QB to run the ball or makes him hesitate because the Sam doesn’t work back to the box.
As the play begins the zone away from the H-back makes the Nose cut off the backside of the Center to take the opposite “A” and the “read” DE takes the dive. This quick movement by the DL forces the QB to pull the ball. Even if the QB reads it wrong and gives the ball to the RB, the Nose and field (read) DE will vice the back. The Will’s gap is overtaken by the Nose and he will “belly key” back into the opposite “A” in anticipation of the cutback. As the play develops he will scrape to the ball (if the QB pulls it, he will scrape to the outside). The Mike steps to his “B” gap and reacts to the zone away. Knowing the DE has the dive, the Mike can scrape to the field and take the QB. The Mike fits inside the pull and makes the QB bounce (unlike power, the Mike fits inside to bounce the play to the safety because this is an arc block). The CS corrects the fit of the Sam. If the Sam widens the safety fits on the outside of the arc-block, if the Sam crashes in on run, the CS fits on the bubble (the “Pop” pass is becoming en vogue, so someone has to cover the screen even if the QB pulls the ball).
Here is a look at an unbalanced jet-stretch against an Under Front:
Conclusion
The answer to the Over/Under question comes down to tendencies. If the offense is a traditional power/counter team the defense should be in an Over Front. When an offense uses 20 pers. to create leverage on to the field, an Under Front may be the way to go. Each front has its positives and negatives. Versus read/option teams it is important to identify the best ball carrier. Setting the front to create the read the defense wants comes down to gap exchange. A DC can set the front to the H-back or the RB. Setting the front to the “H” helps the defense combat traditional runs, but can change the read for the QB depending on where the RB is. As more teams turn to 20 pers. and add RPOs, it is important to stay even and plus-one to each side. The answer to where the defense sets the strength comes down to what the offense is trying to do. Always base calls off tendencies, don’t just “order from a menu.”
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