That two-gap scheme, predicated on behemoths like the Browns' Shaun Rogers (6'4", 350 pounds) and Corey Williams (6'5", 320) taking on multiple blockers up front—and undermined, in part, by Rogers' tendency to shoot gaps instead of clogging them—would be an awkward task for Jacksonville's defensive personnel.
Of the 10 down linemen on the Jaguars' current roster, only tackles John Henderson (6'7", 335), Rob Meier (6'5", 315), and Terrance Knighton (6'3", 325) have the requisite length and lower-body bulk to two-gap. Henderson and Meier, veterans with 18 years of experience between them, would need to redefine their playing styles to fit the scheme.
A two-gap scheme would also have no place for promising third-year DT Derek Landri. At 6'2" and just under 300 pounds, Landri is built to one-gap, attacking the spaces between blockers with his quickness and leverage. He'd be ineffective playing face-up on a center or tackle.
Knighton, though only a rookie, is the key to understanding the Jaguars' experiments with 3-4 looks.
Physically, he has the wide hips and barrel chest necessary to hold up amidst the trash in the middle of a three-man front. But Knighton, a former high school receiver who racked up tackles for loss in college and ran the 40-yard dash in under five seconds at Temple's pro day, also has the athleticism and quickness to one-gap.
That combination of size and mobility has distinguished nose tackles like Dallas' Jay Ratliff and Pittsburgh's Casey Hampton, who man the middle for attacking 3-4 defenses that shoot gaps instead of holding the line like Tucker's Browns.
Between Knighton, Henderson, Meier, and aggressive tackles like Landri and Attiyah Ellison, the Jaguars' three-man fronts figure to look more like "heavy" personnel packages for their one-gap scheme.
Head coach Jack Del Rio's comments in a press conference yesterday suggested as much.
"There's no secret that we're going to experiment with some different fronts," Del Rio told reporters, "just looking to utilize the people we have."
"The bottom line is what we want to be on defense is attacking."
Last year, Jacksonville hired defensive coordinator Gregg Williams—now with the Saints—with that same goal in mind. Williams' predecessor, current Falcons head coach Mike Smith, had installed a conservative scheme that relied on the front four to generate pressure.
The Jaguars hoped that Williams' blitz-happy defense would confuse opposing offenses by bringing pressure from all sides. Instead, players struggled to learn their responsibilities in the complex new defense and were often caught out of position.
This year's shift in philosophy relies less on particular schemes than on the individual talents of Jacksonville's defensive personnel, especially in the group of players who'd be considered 3-4 linebackers.
Justin Durant, Daryl Smith, and Clint Ingram, the team's three projected starters at linebacker in their base 4-3, are versatile-enough athletes to handle the diverse tasks given to linebackers in a 3-4 defense. The Jaguars don't have much proven depth beyond those three, though, making their stable of potential outside linebackers all the more important.
Draft experts pegged Quentin Groves as a hot prospect for teams with 3-4 defenses last year. His speed upfield and lack of every-down size seemed to pigeonhole him into a rushing linebacker role.
Groves has since committed to gaining weight to play better as a down lineman, bulking up to 264 pounds this offseason from 251 in December, but would still be a good fit as a 3-4 pass rusher.
In a 3-4 look, undrafted free agent Julius Williams from Connecticut might be a diamond in the rough.
"He finishes strong," general manager Gene Smith said of Williams. Smith told Jaguars.com's Vic Ketchman that, despite having been primarily a down lineman in college, "[Williams] certainly shows that he has linebacker history."
Weighing a rock-solid 260 pounds, Williams has the athleticism and strength to be a force in an "elephant" role—the strong-side outside linebacker in a 3-4 defense, who usually has more blockers to fight through on his way to the quarterback.
The Jaguars' best rush linebacker, though, would likely be Derrick Harvey.
Coming off a lackluster rookie year, where his biggest impact was made by holding out until Jacksonville's last preseason game, Harvey might be underrated as he enters his second season.
A consensus first-round talent in 2008, Harvey boasted the quickest first step of any end in his draft class. Though New York's Vernon Gholston was acknowledged as stronger, Harvey was considered the draft's most-natural pass rusher.
Even having added 10 pounds to anchor better against the run, Harvey has the skill set to excel in an attacking role as a weak-side linebacker in the 3-4.
The common thread in all of Jacksonville's potential 3-4 fits is that the players are put in position to attack gaps differently than they would in the Jaguars' base defense. If and when they give opponents a 3-4 look, the change should be regarded not as a commitment to the 3-4 as such, but to a new philosophy of aggressive defense.