Who are the most irreplaceable players in the Big Ten? These aren't necessarily the best players, but the guys who teams really can't afford to lose.
Let's take a team-by-team look at who they are:
Illinois: Offensive tackle Jeff Allen. Illinois already has lost one starting offensive tackle to injury in Corey Lewis (ACL), placing a major burden on Allen to protect a young starting quarterback. Allen has started two seasons and should contend for All-Big Ten honors this fall. He drew praise from the coaches this spring for absorbing Paul Petrino's new offense, and he'll anchor the line at weak-side tackle. If he goes down, Illinois likely will turn to Craig Wilson, who has played mostly special teams in his career.
Indiana: Quarterback Ben Chappell. History shows that for Indiana to have a chance at a bowl game, it needs to put up a lot of points. The running game has been inconsistent the past few years, but Chappell is poised to have a big senior season through the air. The Big Ten's third-leading passer in 2009 will have a bunch of weapons at his disposal, led by first-team, all-conference wide receiver Tandon Doss. Indiana has virtually no experience behind Chappell and would turn things over to a redshirt freshman (Dusty Kiel or Edward Wright-Baker).
Iowa: Quarterback Ricky Stanzi. This isn't a knock against backup James Vandenberg, who certainly proved himself last fall at Ohio State. But Iowa is simply a different team with Stanzi on the field, drawing confidence from him through his ups and downs. You could see how much Stanzi meant to his teammates on offense after he went down against Northwestern last November. Although offensive tackle Riley Reiff, defensive end Adrian Clayborn or safety Tyler Sash certainly can make their case to be in this spot, Stanzi is the player who shapes Iowa's success more than any other player. He's got the 'it' factor.
Michigan: Cornerback Troy Woolfolk. Woolfolk provides leadership and some experience in a Wolverines secondary that looks pretty shaky even with him on the field. The thought of Woolfolk being out would certainly raise the anxiety level among Michigan fans. Woolfolk had some good moments last fall and has a chance to be a very solid Big Ten cornerback this year. He also can play safety in an emergency. Given Michigan's lack of depth in the defensive backfield, Woolfolk's presence is crucial.
Michigan State: Linebacker Greg Jones. This one is pretty obvious. Not only has Jones led Michigan State in tackles in each of his three seasons on campus, but he's the undisputed leader on defense. Without Jones' tackling and play-making ability in the offensive backfield, an average Michigan State defense would be a lousy one. Although the Spartans boast some depth at linebacker with Chris Norman, Eric Gordon and incoming freshmen William Gholston and Max Bullough, Jones is the one guy the coaches are counting on for a ton of production.
Minnesota: Safety Kyle Theret. There's not an obvious choice for the Gophers, but the team's defense lost some major experience after safety Kim Royston broke his leg this spring. Theret, who was suspended during spring ball but should return, has started 32 games at safety. He ended the 2009 season on a strong note with two interceptions and a tackle for loss in the Insight Bowl. If Royston can't return or is limited, Theret will have to lead a young Gophers' secondary.
Northwestern: Quarterback Dan Persa. Persa hasn't even started a game for Northwestern, so how can he be labeled as irreplaceable? First off, no other Wildcats quarterback has game experience, while Persa appeared in 10 contests last fall. Backup Evan Watkins remains a bit raw, and Northwestern will have a true freshman, most likely Trevor Siemian, as its third-stringer this season. Persa already has established himself as a team leader, and he would create problems if he went down.
Ohio State: Quarterback Terrelle Pryor. Another easy choice, as Pryor has started 22 of Ohio State's past 23 games at quarterback. Although the Buckeyes have won games without major contributions from Pryor, the offense will be shaped around him more this fall. He'll need to build off of what he showed on Jan. 1 in the Rose Bowl against Oregon. Backups Joe Bauserman and Kenny Guiton lack game experience, and Ohio State would need everyone else to step up around the quarterbacks to survive without Pryor.
Penn State: Running back Evan Royster. An experienced running back can be a young quarterback's best friend, and Royster certainly qualifies as a veteran. He has started the past two seasons for the Nittany Lions, racking up 2,405 rushing yards and 18 touchdowns. Penn State needs big things from Royster this fall as an inexperienced signal caller takes over for Daryll Clark. Backup running back Stephfon Green has shown flashes, but he lacks Royster's consistency.
Purdue: Defensive end Ryan Kerrigan. We'll find out if running back Ralph Bolden is replaceable this season, but Purdue doesn't want to see anything happen to Kerrigan. The senior is one of the nation's top pass rushers, and he's the most experienced member of a defensive line that loses standout tackle Mike Neal. Kerrigan led the Big Ten with 13 sacks last fall and will make life easier for those around him. Aside from Gerald Gooden, Purdue looks a little thin at D-end.
Wisconsin: Quarterback Scott Tolzien. If Tolzien's value wasn't known after the 2009 season, it became even clearer during spring ball after backup Curt Phillips tore his ACL. Tolzien led the Big Ten and ranked 22nd nationally in pass efficiency (143) last season, completing 64.3 percent of his passes. He limits major mistakes and spreads the ball around well to his receivers. Redshirt freshman Jon Budmayr has talent but lacks game experience and looked shaky this spring. Wisconsin would much rather let Budmayr have more time to prepare.