This subject was discussed in detail on the most recent episode of my NFL podcast, “The Call Sheet.” Check it out at the bottom of this article:

When Hal Mumme got the head coaching job at the University of Kentucky in 1997, he took one look at the Wildcats’ schedule and realized something had to change. A slate which included perennial SEC stalwarts Florida, Georgia, LSU and Tennessee would overwhelm the Wildcats, who’d gone 9-24 in the three seasons prior to Mumme’s arrival. Kentucky’s roster was filled with one and two-star players, while the SEC powerhouses were loaded with more heralded four and five-star recruits. For Mumme to be successful, he’d have to find a way to bridge the talent gap.

Fortunately, he had some ideas on the subject.

The traditional approach to offensive football at that time was to align with a tailback, a fullback, a tight end and two wide receivers — otherwise known as “21 personnel” — and to feature power run concepts and play-action passes. That approach used the run to set up the pass, and power runs were all about vertical displacement. In other words, getting my big guys to knock your big guys off the ball so my running back could slam ahead for four or five yards. This was a style for which Kentucky was ill-suited, and would do Mumme little good.

Instead, he installed a system he had developed while working at a similarly under-manned school, Valdosta State University. That system, the Air Raid, ditched the fullback and tight end for two additional receivers. It featured a no-huddle, up-tempo pace and emphasized passing as the primary means of moving the ball. Mumme, and his Air Raid predecessors (primarily BYU coach LaVell Edwards), threw the ball 65-75% of the time, and only called run plays as audibles at the line of scrimmage when the defense presented a favorable look.

The Air Raid passing game consisted largely of plays that got the ball out of the quarterback’s hand quickly, stretched the defense horizontally and vertically, and allowed the quarterback to key on one defensive player who the route concept would put into conflict. Mesh, Stick. Smash, Curl-Flat, Four-Verts, and fast screens to the perimeter comprised the core of the passing attack. The run game was based on the inside zone play, with horizontal motions like jet sweep and read options like zone-read serving as ways to threaten the perimeter.

The results were eye-popping. Mumme’s Kentucky teams put up points in bunches, even against the stellar competition of the SEC. Smaller schools and teams across the country who felt over-matched by their schedules took notice, and soon were implementing their own versions of the system.

By the mid-2000s, the Air Raid and subsequent adaptations of its up-tempo, stretch-the-field philosophy had taken over college football. They were grouped together in a tidy phrase — “The Spread Offense” — which encapsulated its mentality if not the nuances therein. Spreading the field, either by formation or by play concept, was a way to stress defenses by expanding them and then exploiting the seams that would emerge when they were forced to defend the entire width of the field. Schools like Kentucky, which often lost the recruiting battle for the nation’s best linemen, fished for speed instead, luring athletes to their campus with a fast break, “basketball-on-grass” approach. The system was so successful that college football’s blue bloods eventually signed on. Bo Schembechler must have rolled over in his grave when Rich Rodriquez brought his up-tempo spread to Michigan in 2008. Urban Meyer flourished with his version of it at Florida and then Ohio State. Oklahoma — and the Big 12 in general — ditched their run-first systems and began chucking the ball 40 and 50 times a game. The revolution was complete when Alabama, under known traditionalist Nick Saban, began running it too.

Inevitably, elements of the spread worked their way to the NFL. One of the first teams to embrace its principles was the Washington Redskins, who drafted quarterback Robert Griffin III in 2012 and paired him with offensive coordinator Kyle Shanahan. Shanahan had adopted an affinity for zone run schemes from his father, Mike, who had won two Super Bowls in Denver using a zone-based run game centered on the talents of Terrell Davis. In Washington, Kyle Shanahan implemented the zone-read scheme, which Griffin had executed to great success at Baylor, and added the jet sweeps and perimeter screens that were still foreign to most NFL offenses. By the time Shanahan landed a head coaching job, in San Francisco in 2017, these schemes were becoming commonplace. Shanahan built an attack in San Francisco around the core principles of the spread but added a twist to it by finding ways to run them from bigger personnel, which included fullback Kyle Juszczyk and tight end George Kittle. Those players were versatile enough to block inside the box as well as operate on the perimeter, providing Shanahan the ability to run both power and spread concepts without substituting. His system has flourished ever since, providing a much-copied template for NFL offenses in the 2020s.

Below, we see some of the ways in which the Shanahan system stresses defenses by stretching them horizontally. The clip below features a sweep to the short side of the field with a perimeter screen off of “orbit” motion to the wide side:

The defense does a pretty good job of stringing out the sweep. But receiver Deebo Samuel, who is the ball-carrier, is patient and waits for a seam to develop. Inevitably, it does, as the backside defenders pursue too aggressively and open up a cut back lane that Samuel exploits.

You can see in the photo below how the perimeter screen away from the sweep stretches the defense across the field. The three defenders assigned to the perimeter screen are not in position to help against the sweep, so when Samuel cuts up-field there is no backside pursuit to run him down. This horizontal stretch leads to a big play, allowing San Francisco to “get vertical” without actually threatening the defense vertically.

Here’s a different version of the sweep play to Samuel. On this one, the 49ers set a perimeter screen to the left, sending Kittle, their center and the left tackle to block for it. The linemen to the right block for the sweep. This gives quarterback Brock Purdy a two-way pre-snap read. Purdy will count the numbers at the line of scrimmage. If they are advantageous to run sweep, he’ll hand off to Samuel. If there are too many defenders in the box for San Francisco to block, he’ll throw the perimeter screen. The Niners can account for everyone but the safety to the sweep side, so Purdy hands the ball off. Samuel takes care of the safety by running him over as he barrels into the end zone.

Here’s a horizontal stretch using running back Christian McCaffrey. This is outside zone, or the aptly named “Stretch” play, which does just that to a defense. Outside zone is often run from a compressed formation, where the defense packs in tightly to fit the offense. All of the linemen then reach-block the near defender to the play-side, aiming for their far shoulder and attempting to pin them inside. This provokes defenders to fight laterally so they don’t give up outside leverage. The result is often a seam in the run defense, like we see below, as the lateral flow disrupts their prescribed run fits. A good back, like McCaffrey, can easily exploit these seams:

San Francisco takes full advantage of McCaffrey’s receiving chops in their scheme as well. Here, they put three receivers to the wide side of the field, which tilts the defense in that direction. They then use shuffle motion to widen McCaffrey, pushing him out to the numbers at the snap. This isolates him one-on-one against a linebacker, who is no match for McCaffrey on a wicked double move:

The brilliance of this play begins with coverage recognition, as Shanahan understands he has McCaffrey isolated against a backer. He then uses the shift to widen the formation, pulling the backer away from his safety help and into an isolation. All that’s left is for the Niners to play pitch-and-catch, which they do effectively.

Of course, once teams react too aggressively to these horizontal schemes, Shanahan has an answer. You can only swing the ball to McCaffrey on the perimeter so many times before the defense starts flying downhill to stop him. Once they do, the Niners dial up this:

Spread ’em and shred ’em, or so the saying goes.

Of course, it’s not enough simply to stretch a defense. An offense that can’t block on the perimeter, can’t pick up the blitz, and most importantly, doesn’t know how to sequence their play calls in a way that capitalizes on the advantages these schemes create, won’t be effective. San Francisco succeeds on offense because they can do all of these things. And because they combine great schemes and great play-calling with great players. As does Kansas City. And Philadelphia. And Buffalo. Schemes are only a part of the equation. But for the teams who have mastered the other elements of great football, scheme can be the difference-maker.

For some of the best offenses in modern football, then, the horizontal stretch they’ve adopted from the spread philosophies of the early 2000s have allowed them to exploit defenses and become more explosive in the process. Going horizontal has allowed them to become more vertical, both by consequence and design.