After Percy Harvin returned the second-half kickoff for a 29-0 lead in the Super Bowl, what remained was merely an exercise to get the clock to double zeros. How had Seattle’s defense rototilled Peyton Manning and the record-breaking Broncos offense? With big, fast, ill-tempered players, of course, but also with a scheme tailored to the Legion of Boom.

Seattle is predominantly a Cover-3 team — which refers to a four-man-rush zone defense with three defensive backs each aligned in deep-third coverage responsibilities. Normally Cover-3 is played with one safety near the line of scrimmage in what is termed “sky” alignment — wide, nearer the sideline and away from the middle where the most ferocious contact occurs.

When a safety in Cover-3 instead plays the shallow “hook” zone, which is nearer the middle of the field, it is termed “3-buzz.” If a team plays 3-buzz, it better have fast linebackers to cover the wide flat, and a physical safety in the hook zone because his gap responsibilities in run support are that of a linebacker.

In the first half Sunday, against Manning’s 23 pass attempts, Seattle played one of four versions of Cover-3 16 times, and 11 of those 16 were one of two forms of 3-buzz. Manning completed nine of those 11 passes but for just 43 yards — less than 4 yards per attempt. For reference, during Manning’s 263-game career, including playoffs, he has finished at less than 4 yards per attempt for a game just once — during his rookie year.

This aspect of Seattle’s game plan was underscored when Kam Chancellor was briefly injured late in the second quarter. With backup DeShawn Shead on the field Manning attempted six passes, and on the first four of those Seattle played its only four snaps of 3-sky. On none of those six attempts was Shead asked to be an interior hook defender in 3-buzz.

Seattle benefited in three ways from the 3-buzz: One, because Denver relies heavily on shallow crossing routes — and not just to Wes Welker — the Seahawks in zone coverage had a more agile defender aligned within or near the hash marks to defend, and deter, those routes.

Two, Seattle could capably disguise a changeup coverage called “robber.” Base man-to-man, termed “Cover-1” (which Seattle played three times in the first half, including the Chancellor interception), features a five-man rush with a deep free safety helping man defenders. “Robber” is man-to-man coverage with just four rushing but with an additional safety coming from a deep alignment to “rob” shallow crossers. The alignment of this robbing safety mirrors his alignment of 3-buzz coverage.

Seattle played robber just three times in the first half but one was the game’s third offensive play for the Broncos, in which Chancellor uncoiled from deep alignment on Demaryius Thomas, who was rocked some 5 yards backward after catching a shallow cross for a 2-yard gain. That tone-setter required Manning and all his targets to consider the health consequences of their shallow-cross package.

While fans usually favor aggressive blitz schemes — which require man-to-man coverage, the “12s” are learning to embrace the mantra of destructive zone defense: “Give them 5 yards and a headache.” Against the Seahawks it’s more like 2 yards and a ruptured spleen.

And the last advantage of the 3-buzz is that from the same relatively high-safety alignment, Seattle could employ its seldom-used “quarters” coverage — which features all four defensive backs aligned deep with coverage responsibilities adjusting after the snap based upon the verticality of the receivers’ release.

Seattle played just one snap of quarters in the first half but it resulted in, due to a wrecking-ball rush by Cliff Avril, the Malcolm Smith pick-six and, for my money, the play of the game.

Note that Denver had just 19 yards rushing on eight first-half carries as the Broncos were unable to exploit via the run Seahawks safeties who were defending that shallow hook zone. Of course the majority of those occasions that safety was the omnipresent Chancellor, my would-be vote for MVP.