Both Ohio State and Wisconsin got through the non-conference season undefeated, but both have badly underachieved in the conference season so far.
Northwestern suffered home losses to Depaul and Illinois State, among many others, but is now 5-5 in the Big Ten after notching road wins at Indiana, at Wisconsin, and at Minnesota.
Here's a chart showing how each Big Ten team has performed compared to expectations (as calculated using their current Kenpom ratings):
Northwestern's performance, in particular, has been remarkable. Based on the Kenpom profile, they had only a 6 percent chance of winning 5 or more of their first 10 games. Will they regress to the mean? Probably, but who knows.
By contrast, there was a 20% chance that OSU would have 4 or fewer wins, and a 15% chance that Wisconsin would. They already have regressed to the mean after their lucky non-con runs: OSU's overall expected record is 17-5 (which is their actual record) and Wisconsin's is 16-6 (compared to 17-5 actual). Both teams spent three-quarters of the season playing like 1-seeds and the last quarter playing like NIT teams.