The Isolation run, or “Iso,” is about as direct as football gets. A classic I-formation play, it has everybody on the line manhandle the nearest defender, while the receivers shoot inside to pick-up force and fill players. The fullback takes a running charge at an intentionally unblocked or “isolated” linebacker; the tailback takes the handoff at a full sprint and follows this human battering ram through the hole:
“Inserting” the fullback through the line of scrimmage like this creates an extra gap for the defense (especially linebackers) to worry about. And because the tailback can cut to the left or the right of the lead block, deeper defenders on both sides of the formation have to make the right reads. Since Iso’s run into the teeth of the defense, they’re usually short-gainers, though this is compensated for by their playaction potential–it’s hard for linebackers to not creep up when they’ve got two backs making a beeline for them.
I’m a child of the 90’s, so for a long time I considered the Iso play to be football at its purest. It was the greatest common denominator among the top-level teams. The NFL was still largely familiarizing itself with zone schemes, spill defenses, post-steroid era physiques, and spread offenses, an environment that favored the straight-forward Iso and teams like the Redskins and Cowboys, who took advantage of the play. Meanwhile, running-based college programs like Nebraska leaned on the Iso to bludgeon lesser teams into submission, especially at the end of games when the option was an unnecessary risk. (A close cousin of the Iso would be the interior Lead play, which generally asks the fullback to hit the first man he sees, as opposed to seeking out a specific player; note that you’ll sometimes see “Iso” and “Lead” used interchangeably.)
Most high schools, meanwhile, played the same I-formation schemes. Prior to the public adoption of the Internet, it was extremely hard to use new football concepts even if you subscribed to all the latest magazines and regularly attended coaching clinics. Of the two best-publicized schemes of the time—I-formation, passing-tree ball that borrowed from Coryell, and split-back, route-concept schemes associated with Walsh—the I-formation was easier to teach and easier to match talent-wise, so it was either what most coaches knew, or what they could easily pick up.
Iso and Lead plays are more common the further down the ranks you go. To be honest, the only play I remember from JV is “Pro-right, 24 Ice,” which was just a strong-side Iso out of the I. Up by twenty? Run the Iso. Down by twenty (admittedly more likely with waifs like young me blocking)? Run the Iso. It’s easy to see why: the Iso has everyone pretty much blocking straight ahead, so it reduces screw-ups when there’s a lead to protect, and at least lets your team worry about getting their heads straight when things have gotten out of hand.
The Iso (and more general interior Lead plays) had to evolve in order to offset the play’s biggest shortcomings. First, the Iso was vulnerable to slants and stunts because it didn’t put blockers in a position to consistently create favorable angles. Second, the Iso created a relatively small hole for the running back, so if a linebacker was quick he could gum the play up either by jamming the fullback near the line or by slipping the center-guard combo block. For this reason, the classic Iso is now mainly used as a change of pace or as a clock-killer at higher levels of play; if you watched the Ravens wrap-up the AFC Championship and the Super Bowl, they broke out an Iso/Lead play when closing out both games.
Though better known for “student body right,” John McKay’s USC squads, which were coordinated by Don Coryell among others, might’ve been the first to figure out a way to keep lead plays like the Iso working even against eight-man fronts. Coryell and McKay (both I-formation gurus) simply added elements of the draw play. This twist combatted both of the traditional Iso’s weak points. A deeper, delayed handoff meant the running back could read developing blocks at the line of scrimmage and run to daylight; the linemen knew this, so they could pass set and react to the defense, essentially letting the DTs and DEs go wherever they wanted to and take themselves out of the play. Meanwhile, the linebackers had to respect the QB’s deep drop (and the backs’ slight hesitation) by maintaining their depth, which gave the fullback plenty of room to make his block.
The trick to making the play work was that both the fullback and the tailback read the defense. The fullback went to wherever the onside defensive tackle had vacated to meet the linebacker, while the tailback read the entire front for creases and cutbacks; if it happened to be the middle that was open, he read his fullback’s block to determine which direction to cut after clearing the line of scrimmage. It’s easy to see how these reads fed into the evolution of the formal zone run game.
Norv Turner and Ernie Zampese, both Coryell disciples, ran the play with regularity when they served as offensive coordinator for the Dallas Cowboys in the 90’s. It might not be a stretch to say that Emmitt Smith earned his HoF credentials with two versions of this hybridized play called “Iso” and “Lead Draw.” The Cowboys “Iso” was a direct descendant of the classic Isolation play, as it had the fullback draw a bead on an isolated middle ‘backer.
The fullback in this case was the 6’2 Daryl “Moose” Johnston, who routinely served as clean-up man for missed blocks on Iso plays. He was such an effective blocker that it was often advantageous for linemen to miss blocks, because Johnston would pick up loose DTs and free the linemen to occupy the ‘backers, creating a de facto Wham play (back-on-lineman.) Smith, meanwhile, was a savant at reading fronts, and could often cut plays to the backside by three or even four gaps for big gains.