Led by Illinois’ No. 1-ranked unit, the Big Ten has 6 of the top 12 defenses in the country

COLUMBUS, Ohio — Only four Big Ten teams are ranked in the AP Top 25, but six of the top 12 defenses in college football reside in the conference.

The Big Ten’s surprise team this year, Illinois — 17th in the AP poll — has the top-ranked defense in the nation, followed by No. 2 Ohio State, which appears more and more each week to be a complete package.

Michigan (AP No. 4) is ranked fifth in defense. Iowa, unranked in the poll because of a moribund offense, was propped up by its tough defense before running into the speeding Buckeyes last week. The Hawkeyes are sixth in the nation in yards allowed per game.

Rutgers and Minnesota have needed the help of their defenses, ranked seventh and 12th, respectively, to stay above .500.

All six teams are allowing fewer than 300 yards per game. Five of them, with Rutgers the outlier, are giving up fewer than 20 points per game, as is Penn State.

By contrast, only Iowa State in the Big 12 is allowing 300 yards or fewer per game, with Iowa State and Kansas State allowing fewer than 20 points.

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In the ACC, only Syracuse is allowing fewer than 300 yards per game, with Syracuse, North Carolina State and Clemson allowing fewer than 20 points.

In the SEC, Georgia, Kentucky and Alabama are allowing fewer than 300 yards and 20 points. No teams in the Pac-12 can claim either.

Illinois (6-1, 3-1 Big Ten) is the conference’s biggest surprise this season with a defense allowing 221.1 yards and 8.9 points per game. The Illini’s only loss came in a 23-20 setback at Indiana in Week 2 — the most points they’ve allowed all season.

“Really, from the pilots we hop on the plane with to the schools that we talk to, everybody is a lot more aware of Illinois football,” second-year coach Brett Bielema said.

He noted this week that Illini cornerback Devon Witherspoon was named a semifinalist for the Thorpe Award given to the best defensive back in college football. Penn State’s Joey Porter Jr. and Ohio State’s Lathan Ransom also were among the 12 semifinalists.

It’s not a surprise when Ohio State shows off an explosive offense, but the Buckeyes now have the second-ranked defense to go with it.

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Ohio State is holding teams to 239.9 yards and 14.9 points per game.

“I thought the guys were fresh, they were fast and opportunistic,” defensive coordinator Jim Knowles said after the Buckeyes thumped Iowa 54-10 last week.

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Coach Ryan Day lured Knowles from Oklahoma State to overhaul the Ohio State defense, which finished last season ranked 38th in the country.

“We expect these good things to happen by the way we’ve trained and we’ve played,” Knowles said. “And I know it has a great effect on the whole team. Everybody feels confident.”

Safety Tanner McCalister, a graduate transfer who accompanied Knowles from Oklahoma State, had two interceptions as the defense forced six turnovers against the Hawkeyes.

“Like Coach Knowles says, we can win games on defense,” McCalister said. “We don’t always have to rely on our No. 1 offense. We have a pretty good defense, and we can win games if need be.”

AP’s Eric Olson and Tom Canavan contributed.