Blocking for the nation’s best group of running backs, Big Ten offensive lines fared well last season. Will 2015 serve as a reality check around the league?

As spring practice opens in Ann Arbor and Evanston this week, we’re comparing position groups around the Big Ten. Offensive line is next on the list. For others in the series, click here:

Best of the best: Michigan State

The linchpins are back in rising junior left tackle Jack Conklin and senior center Jack Allen, both of whom will land on preseason All-America teams. The pair of Jacks spearheaded the line last year as the Spartans allowed a Big Ten-low 11 sacks, converted 49.7 percent on third down (second to Ohio State) and operated more efficiently in the red zone and in goal-to-go situations than any other Big Ten team. Donavon Clark also returns at tackle. The Spartans lose left guard Travis Jackson, a second-team all-conference pick, and versatile mainstay Connor Kruse. Brian Allen, Kodi Kieler and Miguel Machado appear ready to compete. And these guys will look even better with Connor Cook in command of the offense.

Next up: Ohio State and Wisconsin

A temptation exists to rank every OSU unit as the Big Ten’s best, and the Buckeyes aren’t far off on the offensive line. They lose only right tackle Darryl Baldwin from a group that turned dominant late last season en route to clearing a path to the national title for Ezekiel Elliott and Cardale Jones. Left tackle Taylor Decker, the lone returning starter last year, ranks among the nation’s best at his position, and right guard Pat Elflein earned all-conference honors. Center Jacoby Boren and left guard Billy Price are also back as starters.

At Wisconsin, the cupboard is considerably more empty with the departure of right guard Kyle Costigan, right tackle Rob Havenstein, both All-Big Ten picks, and left guard Dallas Lewallen. Alongside the brilliance of Melvin Gordon, this was the league’s best unit last year. Center Dan Voltz and left tackle Tyler Marz return to anchor the line in 2015. Michael Deiter is ready to go as a redshirt freshman, and the Badgers will find two more starters among a promising group of youngsters.

Sleeper: Michigan

The Wolverines weren’t bad on the line last year. Seriously. OK, at least, it was an improvement over 2013, and all five starters are back to go with, presumably, a much more well designed offensive system. With left tackle Mason Cole, who played as a true freshman, guards Graham Glasgow and Kyle Kalis, center Jack Miller and right tackle Ben Braden, Michigan looks the part. New offensive coordinator and O-line coach Tim Drevno has plenty of tools with which to work. Reserves Erik Magnuson, Logan Tuley-Tillman, Blake Bars and Patrick Kugler give Michigan a chance to develop solid depth this spring. The Wolverines should be better at running back with the addition of Ty Isaac. A breakthrough season across the front isn’t out of the question.

Problem for a contender: Penn State

It was flat-out ugly last year as the Nittany Lions allowed 44 sacks, last in the Big Ten and 121st nationally, and averaged 2.94 yards per rush – 122nd nationally. PSU lost left tackle Donovan Smith early to the NFL and left guard Miles Dieffenbach. Center Angelo Mangiro and tackle Andrew Nelson lead the group of returnees, and Penn added a pair of potential difference-makers in January in freshman Sterling Jenkins and juco transfer Paris Palmer. Four freshmen redshirted last year. Really, there’s nowhere to go but up, but Penn State needs fast improvement from its line to allow QB Christian Hackenberg time to operate. If growth here is slow, so will be Penn State’s offensive progress.