MADISON, Wis. -- By most measures, Wisconsin's 2015 defense will be regarded as one of the best the program has seen in the past 50 years.
The Badgers lead the nation in scoring defense, and rank third in total defense. They can pressure quarterbacks, stuff the run, and frustrate receivers accustomed to finding open space. They have largely lived up to the challenge every Saturday, providing an uneven offense with a safety blanket.
And yet, with Wisconsin (9-3) on the cusp of playing USC (8-5) in the National Funding Holiday Bowl on Dec. 30, questions persist about the validity of those accomplishments. That's because each achievement arrives with the same caveat: Who have the Badgers really played? Fair perception or not, the players are aware that the only way to quell those doubts is with a strong performance against the high-powered Trojans.
"That's an extremely fair question," Badgers outside linebacker Vince Biegel said. "I think a lot of question marks are around, have we played enough high-ranking offenses? Have we played high-caliber teams who would solidify us as a top-tier defense? And I think that's the biggest question.
"I hope we can answer those questions for the fans back home, to solidify ourselves as a top defense by going out against a Pac-12 team who we have a lot of respect for and playing Wisconsin defense. That's all I'm going to say."
Despite Wisconsin's defensive dominance, there are legitimate questions about how the Badgers' statistics were attained:
* Wisconsin held opponents to three points or fewer in three consecutive games for the first time since 1937. But that came against Miami (Ohio), Troy and Hawaii, teams that finished 10-27 collectively.
* Wisconsin ranks No. 1 nationally in scoring defense at 13.1 points per game. But the Badgers' nine victories have come against schools with a combined record of 33-75. Wisconsin has not beaten a single opponent with a winning record, though the Badgers' offense is far more responsible for failing to come through against Iowa and Northwestern, when scoring from the 1-yard line in each contest could have won the game.
* In the team's marquee season-opening game against Alabama, the Crimson Tide scored 35 points and amassed 502 yards of total offense -- by far the highest output Wisconsin allowed this season. No other team had more than 333 yards. Heisman Trophy winner Derrick Henry rushed for three touchdowns and averaged an astounding 11.3 yards per carry, his best mark of the year.
Biegel and linebacker Joe Schobert each said the Alabama game was not indicative of the defense's capabilities. They instead point to the Iowa game, when the Hawkeyes scored just 10 points and gained only 221 yards of total offense. Still, Wisconsin's defense has not played many explosive offenses, and the Badgers' schedule didn't include the four best teams in the Big Ten East.
"The fans say we want a tougher schedule, right?" Biegel said. "Obviously, we play whoever's on our Big Ten schedule. We had Iowa, one of the best teams in the Big Ten, one play away from being in the final four. We have multiple other great-caliber teams we've played. But yeah, I think we have a great matchup for us against USC, and we're really, really excited for the challenge for ourselves and for the fans as well."
Many of those questions can be put to rest if Wisconsin finds a way to stop USC, which averages 34.9 points per game and is the highest-scoring team the Badgers will play this season.
Wisconsin defensive coordinator Dave Aranda said USC isolates its skill-position players better than any team the Badgers have faced this year. Trojans quarterback Cody Kessler (28 touchdowns, six interceptions) excels at quickly diagnosing defenses and throwing the ball to his receivers before he faces substantial trouble in the pocket.
"When there's pressure in his face, he steps up and makes throws," Aranda said. "He's actually better when there is pressure."
Aranda did note that USC's offensive front allows breakdowns -- Trojans quarterbacks have been sacked 35 times, compared to the Badgers' 24. And Wisconsin is keen on taking advantage of those breakdowns.
USC's most formidable skill-position player is wide receiver Juju Smith-Schuster, who has 85 catches for 1,389 yards and 10 touchdowns. According to Aranda, the Trojans will run any number of route combinations for him, from hitches to slants to simply one-on-one deep balls on which he can out-leap defenders.
"They're smaller, shifty guys," Schobert said. "They're explosive. You give them one little crease, and they're going to explode through it. They've got some great lateral quickness. Stuff like that makes you worry about your gaps and stay in your gaps because they can make you pay if you get out of them."
Just how good is Wisconsin's defense? Competing against USC offers an opportunity for the country, and the Badgers themselves, to find out once and for all.
"It would just cap that whole season off," cornerback Darius Hillary said. "I definitely think it would prove to the country that our defense, our team, is one to be reckoned with."