Posted by ESPN.com's Adam Rittenberg
Fifteen spring practices still don't mask all the warts a team has, and every head coach has a position group that keeps him awake at night. After looking at where each Big Ten team got help this spring, here's a look at the positions that still look a little shaky around the league.
Illinois' offensive line -- The Illini boast arguably more offensive firepower than any Big Ten team, but they'll struggle without improvement up front. There's youth throughout the front five, and while players like Jeff Allen boast loads of potential, there are a few unknowns heading into the fall. The line allowed five sacks and 16 tackles for loss in the spring game.
Indiana's wide receivers -- Kellen Lewis' dismissal from the program after spring practice creates a major void at receiver. Lewis was pegged to be Ben Chappell's top target, and with Ray Fisher moving from wideout to cornerback, the Hoosiers need big things from young players like Tandon Doss and Damarlo Belcher.
Iowa's defensive tackles -- This position will be a question mark for the Hawkeyes right up until the season opener, and most likely beyond. Iowa must find a way to replace mainstays Mitch King and Matt Kroul, and it lacks much experience besides Karl Klug. The team needs continued development from guys like Mike Daniels and Cody Hundertmark.
Michigan's defensive line -- Brandon Graham should be one of the nation's top pass-rushers this fall, but he needs some help up front. Michigan likes what it has in young linemen like Ryan Van Bergen, Mike Martin and incoming freshman Craig Roh. Those players will need to grow up fast so the defense can generate consistent pressure.
Michigan State's running backs -- Few players meant more to an offense than Javon Ringer did to Michigan State last fall, and the search for a replacement remains a bit murky. Aside from a brief surge by Ashton Leggett, the running back room remains very crowded as Caulton Ray entered the mix this spring. Two heralded freshmen arrive during the summer in Edwin Baker and Larry Caper.
Minnesota's offensive line -- The Gophers have the bodies up front, but they've still got a long way to go in picking up the new offensive system/philosophy. It's a fairly dramatic change for returning starters like Dom Alford and Ned Tavale, so growing pains are expected. But a talented Gophers team can't take another step forward if its offensive line doesn't come together.
Northwestern's wide receivers -- Three starters are gone at receiver, and no one really wowed during spring practice. Northwestern should get better here as Jeremy Ebert returns from hip surgery, but it's time for experienced players like Andrew Brewer and Sidney Stewart to step up as primary targets for new starting quarterback Mike Kafka.
Ohio State's offensive line -- Michigan transfer Justin Boren undoubtedly had a positive effect on the offensive line this spring, but questions remain about a group that underachieved for most of 2008. Can Mike Adams complement his physical gifts with a toughness needed to play left tackle in the Big Ten? How will Jim Cordle and Bryant Browning adjust to new positions when the games begin? Stay tuned.
Penn State's secondary -- Head coach Joe Paterno didn't hide his concern for this group, which lost all four starters from 2008. Breakdowns in the secondary doomed Penn State in its only two losses last fall. Safety Drew Astorino should be ready for big things, but cornerback A.J. Wallace must find a way to stay healthy and become a legit shutdown guy on the outside.
Purdue's quarterbacks -- Joey Elliott boasts the knowledge to be an effective Big Ten starter, but does he have the skills to get it done? He has spent a lot of time on the sideline during his college career, and Purdue would benefit from having another viable option at quarterback. Justin Siller's dismissal really stings, and the development of backup Caleb TerBush looms large this summer.
Wisconsin's linebackers -- The Badgers lose a lot of production in DeAndre Levy and Jonathan Casillas, and they don't have much proven depth at linebacker. They can ill afford an injury to Jaevery McFadden or Culmer St. Jean, and it's imperative to develop more linebackers during preseason camp.