Is this the first time that MAC teams have defeated three B1G teams in the same season? I can't remember when this happened before, but my memory is very fallible.
The wins this year were:
Buffalo 42
Rutgers 13
EMU 20
Purdue 19
Akron 39
Northwestern 34
It happened as recent as 2014:
Indiana 42
BG 45
NIU 23
Northwestern 15
CMU 38
Purdue 17
BG also turned right around and won two more games vs the Big Ten the next year in 2015 with a pair of road wins over both Maryland and Purdue. I don’t think any other MAC team beat a Big Ten team that year though other than BG.