Thomas Sirk is Duke’s starting quarterback heading into the Blue Devils’ matchup Saturday with No. 23 Northwestern, and that’s about all the Wildcats know about the recently promoted junior.

Sirk ascended to the lead job this fall after the graduation of Anthony Boone, and has attempted just 76 passes in his career. Add in a Duke offense that NU coach Pat Fitzgerald described as “pretty vanilla” through two weeks, and the Cats don’t have much to work with in figuring out Sirk.

The Blue Devils’ signal caller has looked formidable thus far, completing 68 percent of his passes for 604 yards and tossing five touchdowns with zero interceptions. He’s also shown ability as a runner, carrying 24 times for 154 yards and a score.

But Sirk piled up those numbers against two decidedly outmatched opponents in Tulane and North Carolina Central, which complicates any evaluation of his play. Similar to NU’s romp over Eastern Illinois, the Duke coaching staff didn’t have to push any boundaries with Sirk to secure victory.

And going back to 2014, Sirk played only sparingly as a change-of-pace running quarterback behind the incumbent Boone. Any edge the Cats hope to gain from scouting will have to come from knowledge of Duke’s preferred schemes.

“We’re going to have to get ready to play their plays and play their formations,” Fitzgerald said. “Offensively, similar to things we’ve seen from other opponents, they’re a gap scheme, power running game and quarterback run game, play action pass off of it.”

That offensive philosophy is typified by a play from the third quarter of Duke’s contest against Tulane. The Blue Devils line up in a spread formation and run the read-option. The left guard (No. 67 in white) pulls around the line to sell the idea of an outside sweep play with the running back, only to have Sirk keep the ball and scamper past Tulane’s linebackers, with the help of some excellent blocking up front, for a nice gain.

This kind of play is designed to catch defenders out of position, and can also be used to set up play fakes to open space downfield in the passing game.

That’s exactly what happens on this play against North Carolina Central. Sirk fakes to the running back, then throws a bomb to a wide-open receiver for an easy touchdown. It helps here that the Duke receiver completely abused an overmatched cornerback, but Sirk also delivers a perfectly placed pass to hit his man in stride. It’s a likely completion ever under much tighter coverage.

Blue Devils coach David Cutcliffe is a noted quarterback whisper, having most famously coached both Peyton and Eli Manning in college, so it’s no surprise that he’s maximized Sirk’s talents as a thrower.

But Sirk started his career as a runner, and his versatility seems to be the focus of the Cats’ defensive game plan. The onus of containing a running quarterback often falls on a team’s linebackers, and sophomore Anthony Walker will have to keep up his strong play in the middle for the stop unit to succeed.

“A dual-threat quarterback keeps you on your toes,” Walker said. “He can always pull it down and run a little bit, but you can’t get too intrigued on his running ability.”

Having Walker roaming the middle of the field certainly helps, but NU’s ace in the hole is more likely to be its revitalized pass rush. Sirk hasn’t seen much pressure, being sacked just once so far this season, while the Cats’ pass rush has gotten to opposing quarterbacks six times.

And the threat of a running quarterback is nothing new to NU’s veteran line.

“We face a lot of those guys in the Big Ten,” senior defensive end Dean Lowry said, “but especially us, facing guys like Clayton (Thorson) and (Matt) Alviti throughout camp.”

Lowry, an Academic All-Big Ten selection, also noted the “huge correlation” between getting pressure on the quarterback and winning the game. If the Cats can flood the backfield and get to Sirk early and often, they’ll neutralize his dual-threat ability and tilt the odds in their favor.

But that’s easier said than done against an unpredictable offense that almost certainly has some surprises in store for its first Power 5 opponent. The most important battleground may be on the sidelines, where defensive coordinator Mike Hankwitz and the rest of the coaching staff will have to improvise to stop whatever the Blue Devils throw at them.

“We anticipate doing a lot of adjusting,” Fitzgerald said.

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