Xs and Os from the proprietor of the essential Smart Football. As part of the Doc's ACC Week.

You could successfully argue that the spread offense, both in its run-first and pass-first incarnations, was invented to counter the aggressive, eight-man front defense Virginia Tech made famous. In the nineties, many teams tried to emulate Frank Beamer and defensive coordinator Bud Foster's scheme, with its premium on defenders stacking the line to either stop the run or scare the offense into abandoning it and apologizing for having considered such a silly idea. Yet the spread has effectively run the eight-man front out of college football -- at least as a base defense -- with its reliance on quick, easy throws, quarterback runs and "speed in space" philosophy.

But here's the rub: While the defense Virginia Tech made en vogue was effectively countered, the actual schemes Beamer and Foster have put into practice in Blacksburg have evolved, year-in and year-out, to maintain the most dominant defensive legacy in the country: Since joining the ACC in 2004, the Hokie D has rebounded from subpar years in 2002 and 2003 to finish in the top-10 nationally in both yards and points allowed five years in a row -- despite overhauling their base defensive scheme, to zero fanfare. To understand what the Hokies do now, it helps to first understand what they used to do.

The 4-4 "G" and the "Robber." Virginia Tech was long known as an exemplar of the eight-man front. While many commentators talk about such fronts in terms of simple arithmetic, for Virginia Tech, it was both a scheme and a philosophy. They called their particular scheme, which was first refined at the University of Washington under its former defensive coordinator and head coach Jim Lambright, the "G," and it was a variant of a "4-4" front. This meant that there were four defensive linemen, four linebackers (two inside guys and two outside guys, still colorfully refer to as the "whip" and the "rover") and three secondary players: two corners and a free-safety. The name, "G," referred to the specific alignments of the defensive line and linebackers:

From this eight-in-the-box set, Tech used all manner of blitzes and devices to get defenders into the backfield. They also used all the common pass coverages, like Cover 1 and Cover 3 (the number usually refers to the number of deep zone players, i.e. "Cover 3" is literally a "three-deep" coverage). But Beamer and Foster also relied on a hybrid coverage of their own design: The "robber," run out of the "G" front. This coverage worked so well because it transformed an already run-heavy eight-man front into a nine man front, where they combined their 4-4 set with conventional two-deep principles: Instead of two deep safeties, they used two deep cornerbacks who split the field into halves. The free-safety then was free to play a "robber" technique -- that is, on pass plays, he read the quarterback's eyes and broke on intermediate routes, but on runs, where he truly became valuable, he was an incredible ninth run-stuffer in the box.

Although not the best against the pass, that wasn't the point. It was good enough (especially with dynamos like D'Angelo Hall at cornerback), and the focus was on stuffing the run or hitting the quarterback before he could release the ball.

Unsurprisingly, against such a stacked fronts teams didn't have a prayer of running against the Hokies, and every play seemed like an avalanche of defenders. Also unsurprisingly, however, offensive schemes began to change.

Taking the spread on, head on: Cover 4 from the "G." Obviously, the narrative over the last decade in college ball has been the rise of "the spread," and, good as it is, the 4-4 "G" with the "Robber" was not designed for the spread offense. With only three secondary players, the defense was limited in what coverages it could use and disguise. As Bud Foster recently told ESPN's Mark Schlabach, "Back when they played two tailbacks, you could put eight or nine guys in the box. Now they're making it tougher to do that because of where they place their people." And so, he explained, with offenses "putting five or six athletes out in space," the Hokies too had to "put athletes out in space."

He and Beamer did so by converting his "Rover" outside linebacker, already a hybrid player who sometimes looked more like a strong safety, into a full-time defensive back. This allowed him to make also made a dramatic switch away from the coverages they had used -- i.e., man-to-man with a deep free safety, or two-deep with the corners -- to basing from a "cover 4" or "quarters" coverage.

As with other coverages, the "4" in cover 4 refers to the number of defenders dropping into deep zones -- in this case, four guys, both corners and both safeties. But don't confuse this adaptation with "prevent" coverage: It's a whirl of contradictions -- a zone defense with man-to-man principles, and a defense with four secondary players that can still present a nine-man front against the run.

"Quarters" can be a four-across deep zone, it can double-team a dangerous wide receiver, or it can be straight man-to-man. Which the defense employs on any given play is determined by what the offense does. For example, if the offense splits out two wide receivers to the same side of the field, and both run straight up the field on deep routes, the safety plays man on the inside guy and the cornerback plays man on the outside guy. If, however, the inside receiver were to run immediately to the flat -- say, on a bubble screen -- while the outside receiver ran upfield, the corner and the safety would actually double team the deep man, defending him from both the inside and the outside. This type of read-and-react is great against the spread's multiplicity, as it can allow some very short completions but lead to lots of interceptions and few downfield passing windows.

Et, tu, nine-man front? But what of stopping the run? The advantage of the old 4-4 "G" and "robber" was as a run-stuffing defense with basically a nine-man front, and don't many spread teams spread to run?

What makes Tech's "quarters" coverage particularly interesting is that they have not actually changed their old "G" front, they have merely removed one guy from the box and lined him up at safety without changing his aggressive responsibilities against the run. Below is how Virginia Tech lined up against Kansas's spread in the 2008 Orange Bowl. (A loss that exemplifies the achilles heel of the Hokie defense: the Hokie offense. It's tough to win games when Tyrod Taylor and Sean Glennon combine for three interceptions.) The Hokies lined up in their base quarters look from the "G," merely moving the former "Rover" (circled) to safety, while moving the "Whip" outside, over Kansas' slot receiver; this formation gives the offense very little information, and in fact, with Jayhawks' motioning an extra blocker into the backfield for a run to the left, is inviting for a run, with six blockers in the box against six defenders:

The runner, Jake Sharpe, took the ball while the near safety (the Rover), seeing that no Jayhawk receivers are releasing downfield, attacks the line. Note that Kansas is not unaware of this tendency, as they send a receiver over to block the safety rather than the cornerback.

KU's line and lead blocker execute their blocks, and the runner cuts through the hole for what looks like it could be a solid gain, but the safety beats the receiver's: it is mano-a-mano now ...

... and the end result is the gain of about a yard:

The play was well-blocked from Kansas' perspective, but even though the numbers before the snap matched up in the Jayhawks' favor, Tech's aggressive philosophy in the secondary ruins the usual math.

Tech relies heavily on its safeties to be sure tacklers, but just the threat of aggression leads to problems for the offense and opens things up for the rest of the defense.

The moral here is that Beamer and Foster have continued to stay a step ahead of offenses, and have done so by keeping their eyes wide open, and knowing when changes in the way offenses was played was imminent. As Foster also told ESPN of the spread, "I think it's here to stay ... I don't think it's a fad. It's just part of the evolution of offense." But neither is the Hokies defense a fad, nor a fluke that just stacked the box when everyone was running the ball out of two backs. Defense is just old principles applied to new situations, and so it is with Virginia Tech, where, through disguises, a new base look, and some principles from their old stuff, the Hokies can year-in and year-out dominate with the "Lunch Pail Defense." The schemes might change, but the mentality -- and the results -- haven't.

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Chris Brown writes the strategy and philosophy site Smart Football. You can reach him spreadattack at yahoo, etc.