Standing on opposite Michigan Stadium sidelines today, Michigan coach Jim Harbaugh and Illinois coach Lovie Smith will make history: It will be the first time previous Super Bowl head coaches will face each other in a college game.

The pro-to-college transition is uncommon, especially for NFL coaches who have had success.

According to the Associated Press, only six of the Football Bowl Subdivision teams are led by former NFL coaches.

For Smith, who coached the Chicago Bears to the Super Bowl following the 2006 season, it was simply about a new experience. He coached the Bears in 2004-12 and the Tampa Bay Buccaneers in 2014-15 before being fired.

"Coaching college ball in general after you've been in the NFL for so long is doing something different," Smith said this week. "My last few stops in the NFL didn't turn out the way I wanted it to, but I'm a football coach, and I spent a lot of time in the state of Illinois, so it just seemed like a natural fit.

"From my time in Chicago, I looked at what the University of Illinois had done. I thought they had a lot of potential. I feel that way still, so those were some of the reasons. It was the right fit at the right time."

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Smith making the move at 57 after 20 years away from college football was a significant leap.

Most pro coaches are more detached from pro players, who are more mature, often have families and need less direction. Though that business-like approach appeals to many coaches, some prefer the higher level of interaction college provides.

"More than anything, it was a chance to coach young men that were at a point in their life where you could offer them some guidance on the field and off the field to reach their goals," said UCLA coach Jim Mora, who spent nearly 25 straight years as a professional coach, including stints as head coach in Atlanta and Seattle. "It's very rewarding to work at this level. I'm very grateful and very happy and fortunate to be here."

When Harbaugh was pondering an NFL-to-college transition in December 2014, many pundits pointed to his disdain for recruiting, that he would have no interest in chasing high school kids. The past two years have shown that's part of the job that fuels him, on the road, meeting players and families, experiencing different parts of the country.

And the ability to have a hand in all aspects of the program. after having someone else choose your players in the NFL, also is appealing.

"There are just things that are different," Smith said. "I wouldn't necessarily say so much harder. There's no recruiting in the NFL, and there's recruiting in college. Besides that, (it's similar). You have a period of time. You're trying to get the guys to (follow). You're trying to teach them as much as you possibly can during that period of time, trying to get players to play up to their potential. A certain way you want them representing our university the way we want NFL players to represent the organization. Dealing with people, teaching them the basic fundamentals of football and going from there."

Mora saw "tons" of differences.

"Not necessarily on the field, other than the tempo stuff," he said. "But you're limited in the amount of time that you can spend with the players, because they do have school and you don't deal with that in the pros. You're dealing with younger athletes, so a different level of maturity than you are with NFL guys. But the football part is the football part. It's the other things, and I really enjoy the other things."

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Things like location and comfort. Harbaugh grew up in Ann Arbor, attended U-M and often has explained how he loves sharing his city with his young children.

After struggling with the Washington Redskins, Steve Spurrier came to South Carolina because he knew the SEC, but also because he loved golf, and some of the nation's best was nearby. Smith pointed out he knew the Midwest and Illinois. Mora grew up in Los Angeles and still had family in the area, so that eased the transition.

Harbaugh has filled his staff with NFL-experienced coaches, still appreciating the league's impact.

But there are exceptions to every rule.

One coach who left abruptly and likely burned that NFL bridge: Louisville's Bobby Petrino. He departed the Atlanta Falcons in the middle of his first NFL season in 2007 (having replaced Mora, who was fired) and is on his third college job since.

"That was a long time ago," Petrino said this week when asked about why he returned to college. "I'm just worried about playing North Carolina State this weekend. ... I don't have any answers for anybody else's decisions to do things, so I really don't know."

Today's game features coaches who nearly reached the professional summit of the sport and still realized they could find another way to enjoy it.

This article was written by Mark Snyder from Detroit Free Press and was legally licensed through the NewsCred publisher network.