Illinois: Scheelhaase, O'Toole
Indiana: Coffman/Sudfield/Roberson (all have at least 50 attempts and ratings of 124.9 or better)
Minnesota: Gray/Shortell
Ohio State: Miller/Guiton
Northwestern: Colter/Siemian
Purdue: TerBush/Marve
Wisconsin: Stave/O'Brien (Biels pulled the trigger on Stave a while back, and have played well since)
Penn State, Michigan, Nebraska and Michigan State have all used their starters almost exclusively. Ohio State would also be on this list if Miller hadn't gotten hurt.
BUT, Guiton demonstrated he's capable with his performance yesterday. The other backups may be capable, too. But they haven't really been needed.
Iowa is the ONLY Big Ten team whose backup QB has logged ZERO PT this year.