If there was one loss in the history of college football you’d like to reverse the outcomes of, which game would that be? 

I’ll go an absolute curve ball here:

2013 Michigan State vs Notre Dame; Notre Dame wins 17-13

With a Michigan State win here, the B1G Championship against Ohio State is almost guaranteed a top 5 matchup, and the winner is going to the National Championship. I have a strong opinion that Michigan State could have beat Florida State and end this argument that the B1G is a weak conference. With Ohio State winning the title the year after, the B1G would have back to back national championships since before the modern era. 
 

For one that more directly affects Ohio State but really doesn’t change much, you could go Iowa vs Michigan in 2016. Iowa won on a last second field goal. With Ohio State beating Michigan the next week, the two teams tied atop the East were Ohio State and Penn State, and Penn State won the tiebreaker due to the win earlier in the season. If Michigan beats Iowa, it’s a three way tie and I believe Penn State’s second loss would knock them out and Ohio State’s head to head win over Michigan would send them to the title game against top 10 Wisconsin. Could this game prepare Ohio State better for Clemson? I think it could be worth talking about. 

(Mod Edit: Moved to the College Sports Forum.)