I investigated Big Ten football crossover games from the past several years and made the following observations:

1.  From 2016-2021, starting when the Big Ten went to 9 conference games, each East team played 1 West team every year and 2 others on a rotating basis (except for some 2020 exceptions).  I am not sure why teams other than Indiana and Purdue (which have a protected rivalry) were playing the same crossover opponents each year.

2.  These repeat crossover games prevented teams from playing other crossover teams more often.  If Indiana-Purdue were the only repeating game, then Ohio State would play each West team other than Purdue 4 times every 9 years and Purdue 3 times in 9 years.  As it was, Ohio State played Nebraska 6 times in 6 years and other West teams twice during that span (not counting Big Ten Championship Games or 2020 modifications).

3.  Ohio State was the only team to sweep its initial round of crossover games.  Results were as follows:  Ohio State 6-0 over Nebraska, Illinois over Rutgers 4-2, Penn State over Iowa 4-2, Minnesota-Maryland 3-3, MSU-Northwestern 3-3, Wisky-TSUN 3-3, Indiana-Purdue 2-2 (no game in 2020 and yet to play in 2021).

4.  The next round of crossover games is as follows:  Ohio State-Wisky, Indiana-Purdue, Maryland-Northwestern, Rutgers-Iowa, MSU-Minnesota, TSUN-Nebraska, Penn State-Illinois (seriously, Penn State gets Illinois?).  These games run from 2022 to at least 2025.  It is unclear if these will be 4- or 6-game series, as the Big Ten has not released schedules later than 2025.  There could be a potential reduction to 8 conference games at some point (hopefully not) pending the Big Ten/ACC/Pac-12 hullabaloo.