LOS ANGELES -- Every scheme has its linchpin.
Football's 3-4 defense can't function without a burly nose tackle to clog gaps, allowing speedy outside linebackers to rush the passer. The West Coast offense relies on the quick reads and timing of a quarterback. And the Tampa 2 needs a speedy, all-knowing middle linebacker -- or Mike -- to roam the heart of the field.
The Trojans are implementing a variation of the famed Tampa 2 defense. Overseeing the transformation is none other than the creator of the defense, legendary defensive coordinator Monte Kiffin.
"In less than 10 words, the Mike linebacker of our defense is basically the quarterback of our defense," says USC linebackers coach Joe Barry, who spent two years working under Kiffin with the NFL's Tampa Bay Buccaneers.
"He is responsible for getting everybody lined up, for getting all the checks, anything that we change at the line of scrimmage, any adjustments that we have when the offense motions or anything -- he's responsible for all of that."
The Trojans are still trying to figure out who that might be. For much of spring practice, first-year coach Lane Kiffin (Monte's son) has held an all-out competition at the Mike spot between sophomore Devon Kennard and redshirt junior Chris Galippo. Many expect Kennard to be the starter come September, but coaches insist no decisions will be made until the week of the season opener.
Both players are preparing to play the position. Kennard, a heady player by all accounts, came to USC as the No. 1-ranked defensive end in the class of 2009 but switched to strongside linebacker with four games to go last season. The Kiffin regime moved him over to the Mike before spring practice -- a decision influenced in no small part by Kennard's high football IQ and willingness to learn, according to Barry.
"That factored in," Barry said. "You can't rely on a guy for all the things a middle linebacker has to do if he's a knucklehead."
Galippo is experienced at the Mike, having started there all last season. Throughout the 15-practice spring schedule that began in late March, he has welcomed the coaching staff's challenge, saying and doing all the right things. On top of staying healthy for the entire spring for the first time, Galippo has also proven responsive to coaching experiments -- including Tuesday's that had him take in roughly 15 snaps at the strongside linebacker spot.
It's not a permanent switch, but it eventually could be.
"The good thing is that I'll always know that middle linebacker spot," Galippo said. "And I trust the coaching staff. They're going to get the best three linebackers on the field and the best three players on the field -- that's their job, and I'm sure they're going to do it."
Scheduled for noon at the Coliseum, Saturday's spring game will go a long way toward determining the summer depth chart. But, as Lane Kiffin stressed in practice this week, any chart the staff produces this early will be in pencil.
"It's not over yet," says Kennard, the son of former Dallas Cowboys guard Derek Kennard. "Spring ball's over, but I'm gonna be working in the offseason, working with the playbook, just learning. I'm always learning. At the middle linebacker position, you're forever learning."
Galippo's situation will be different. He'll continue to work at the Mike while simultaneously picking up the intricacies of the strongside -- or Sam -- position. Compared to everything he had to study at Mike, he said, learning Sam will be like going on a vacation.
"The Sam linebacker's a little different," Galippo said. "You're playing in a lot more space, you're flexed out on receivers a lot, you rush a whole lot more. Obviously, the Mike linebacker's in the middle of everything.
"From experiencing it, I think at Sam, you've got a little bit more time to think and react; whereas Mike, you've gotta go, now. If you take the wrong step, you're beat a lot of the times."
Of course, Galippo faces competition at Sam, as well. Fifth-year senior Michael Morgan, who many say is the fastest member of USC's defense, has done everything asked of him this spring after losing his outside job to Kennard last season. Entrenched opposite him is senior Malcolm Smith, the Trojans' most reliable linebacker in 2009 when he was healthy. Smith appears to be the only lock at linebacker, assuming the right ankle he hurt last season stays healthy.
Depth behind the presumptive starters is scarce at best. Only redshirt junior Shane Horton has game-situation experience at linebacker. Because Frankie Telfort's career ended before it started because of a heart condition and Jarvis Jones' career looks to be over because of a nonspecific neck injury, redshirt freshmen Simione Vehikite and Marquis Simmons are the only other two scholarship players -- and both are works in progress. Junior college product Glen Stanley and L.A. Crenshaw High's Hayes Pullard will enter the fray during the summer.
But, as of now, the USC coaching staff is focusing on what it knows. And the coaches know both Kennard and Galippo could excel at middle linebacker this season -- and having both doesn't hurt.
"I think we've proven that we have two really good Mike linebackers now," Barry said. "Yeah, you can't play with 12 guys, but we're not at that point yet."
Monte Kiffin -- now listed as assistant head coach with USC -- spent 26 years as an assistant in the NFL, but he hesitates to compare any of the USC linebackers to professionals he coached. Perhaps the most famous pro middle linebacker he coached was Shelton Quarles, an athletically ordinary undrafted free agent who developed into the prototypical Mike under a decade of Kiffin's tutelage.
"Shelton Quarles -- he was a special guy, really something," Kiffin said. "I don't put these guys into categories like pro guys, but I think Chris is really working hard this spring because he knows he didn't play as well as he could've last year, and Devon's got a lot of potential."
Kiffin stresses Pac-10 teams will not see the same defense he ran at Tennessee or with the Buccaneers -- "Oregon would love to see the Tampa 2," he said after last Saturday's scrimmage -- but admits several key parts will be similar.
The gang-tackling mentality won't change a bit. The importance of speed won't be forgotten. Roles will be much the same.
Defensive tackle Jurrell Casey will be asked to parallel Warren Sapp as a pass-rusher from the under-tackle spot. The roles of sophomore safeties Jawanza Starling and T.J. McDonald probably will be limited to holding down their side of the field and providing a hard hit or two. And Kennard or Galippo -- one of the two -- will be asked to roam the middle of the field.
"Regardless of what we're doing schematically, the swarm, the hustle, the mentality -- that's all there," Galippo said.
Pedro Moura is the author of the USC Blog for ESPNLosAngeles.com.