Undefeated Wisconsin has outscored its three opponents, 145-14. The Badgers are off a smashing victory against Michigan last Saturday. All of this contributes to a very inflated line for this matchup. 
The Wildcats beat the Badgers by 14 points last season. Northwestern has played  Wisconsin extremely tough during the last four years, winning twice and losing by 14 and nine points, respectively, in the other two games. 
Northwestern's Pat Fitzgerald is one of the top 'dog coaches in the country. The Wildcats have covered 11 of the past 14 times they were road 'dogs. That strong record would be even more impressive, but the underdog Wildcats suffered a horrendous ATS bad beat in the closing seconds against Stanford in their opener on a safety with 20 seconds left. 
The Wildcats are 15-2 in their last 17 Big Ten games. One of those losses occurred to Michigan State by 21 points at home last week. That's another contributing factor explaining why this line is overinflated. 
Northwestern is 9-4 ATS following a defeat. They shouldn't lack motivation after being embarrassed by Michigan State. The Badgers, on the other hand, are fat and happy having steamrolled Michigan. They aren't going to be taking Northwestern as serious as they did the Wolverines.