I've played in leagues where this has been done. I dont like it, but that's the way it is. In the Grand Rapids area I've played in leagues that used both size balls, and also in leagues that just used the larger sized ones.
"The University of Illinois is also in turmoil. The university sports an Interim Chancellor, an Interim Athletic Director, and an Interim Football Coach; the game will be played at Soldier Field, making this an Illini Interim Home Game."