Nobody noticed it until the B1G Championship Game.

Most of the year was spent praising Wisconsin’s stellar defense. It allowed just 15.5 points per game and ranked second nationally against the run and in interceptions. By those stats, there wasn’t much to critique.

It wasn’t even until the second half, when Penn State racked up 211 passing yards and scored 24 points, that the biggest weakness of Wisconsin’s defense was hidden behind some of the best numbers in the country. But Trace Mcsorley and the Nittany Lions receivers exposed a vulnerable secondary on that championship Saturday in Indianapolis.

One of the nation’s best defenses was losing jump balls, missing tackles and getting beat deep. The flaws of the secondary – the one that had 21 interceptions – finally showed.

That’s a major concern heading into the Cotton Bowl.

Why?

Corey Davis.

Western Michigan’s All-American receiver is precisely the type of player the Badgers secondary has struggled with all season long.

Remember how Georgia State was within six points of knocking off ninth-ranked Wisconsin in late September? Sure the Badgers were dealing with some injuries and Corey Clement didn’t play, but the defense also had trouble containing the Panthers’ leading receiver Robert Davis.

He caught eight passes for 93 yards in Madison. But it was plays like this the Badgers had trouble defending:

Look familiar?

It’s not identical to what Penn State did in Indianapolis, but those “go up and get it” type of passes were thrown frequently throughout the contest:

Plays like that sunk the Badgers in the B1G Championship Game. Receivers with excellent body control and a nose for the ball have been a nuisance for Wisconsin’s secondary. That’s why WMU’s Davis can be so dangerous in the Cotton Bowl.

There’s a reason he caught 91 passes for 1,427 yards and 18 TDs this season. His 6-foot-3, 215-pound frame is hard to contain, especially for a player that possess his combination of athleticism and speed.

But the most dangerous aspect of his game is his ability to win those jump ball situations. You know, those same plays that has flustered the Badgers all season?

He went over the top of a Ball State receiver earlier this year to haul in a touchdown grab:

Maybe it isn’t quite in the same category as Noah Brown’s behind-the-back catch in Ohio State’s win over Oklahoma, but it comes pretty close.

That’s not the only threat Davis brings, though.

Davis runs routes hard and can turn short passing plays into long gains. This year, 46 of his receptions have gone for 10 yards or more. Eight times he’s caught a pass for 40 or more yards.

If you don’t recall, Wisconsin had its hands full trying to keep Penn State from making big plays.

He’s got the ability to elude defenders in the open field and has an innate ability of making guys miss. In that same game against Ball State, Davis made three Cardinals just look silly on his way to the end zone:

It’s fair to say that Davis hasn’t lined up against a defense better than what he’ll see in the Cotton Bowl. Sojourn Shelton, D’Cota Dixon and Leo Musso play as aggressively and opportunistically as any secondary in the country. Combined, they accounted for 13 of the Badgers’ interceptions this season.

Finding openings against those three isn’t an easy chore.

But it’s also fair to say that Wisconsin hasn’t defended a receiver as talented as Davis.

That’s the scary part for Wisconsin.

Some of the conference’s top receivers posted big days against that defense. Northwestern’s Austin Carr caught 12 passes for 132 yards and a TD. DeAngelo Yancey had six catches for 155 yards and a pair of scores for Purdue.

Davis is a bigger threat than either of those receivers. And he’s probably got a better quarterback, too.

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Zach Terrell has thrown for 3,376 yards and 32 TDs this season and has completed passes at a nearly 71 percent clip. He’s only thrown three interceptions this year, two of those coming in the MAC Championship against Ohio.

Make no mistake, Wisconsin is in the Cotton Bowl because of its defense. It’s the biggest factor in a 10-win year that notched the Badgers another B1G West title.

It’s also the reason there are no flights from Madison to Pasadena this year.

Wisconsin couldn’t shut down the big play against Penn State. It’s going to have to against Western Michigan.

If not, Davis and the Broncos will be rowing the boat back to Kalamazoo with a Cotton Bowl Trophy onboard.