Ivan Maisel has an interesting piece on the roots of the Fielding Yost and Knute Rockne feud. It's a concise snapshot of the roots of the rivalry, and good fodder for the "slow season" we're in right now. The article is here: http://espn.go.com/college-football/story/_/id/7954463/hate-fueled-football-great-rivalries .
I've always enjoyed the rivalry, finding the Irish to be one of the classier rival fan bases, and less prone to cooler-pooping and couch-burning than some fan bases. Yost's delight in running up points and pissing off opposing coaches with a sharp tongue makes me think of him as an earlier-day Steve Spurrier type.
Choice bits from the Maisel article include:
When Yost became head coach in 1901, he transformed the Wolverines into the most dominant program in the nation. Michigan didn't lose a game under Yost until 1905. These were known as the "Point-A-Minute" teams, both for their margins of victory and to reflect the head coach's personality. Chicago sportswriter Hugh Fullerton would describe Yost's methods as "tramp on the injured and hurdle the dead."
Yost believed Rockne cut corners in recruiting, promising employment and scholarship aid that the rules did not allow and looking the other way when Irish players participated in pro football games on the side.


...punch as I was about to post this myself.
MVictors.com has several outstanding treatments of this topic that shed some additional light, including much that's offered by John Kryk, author of Natural Enemies:
So what was the feud all about? Undoubtedly there was some anti-Catholicism in spite of his protestation to Rockne that:
But ultimately, it was about Yost's conclusion that Notre Dame simply flouted the rules. Yost was ruthless about protecting the Michigan program and fighting anyone who dared to upset its dominance. He clearly felt that Notre Dame ran a program that gave it advantages over its competitors (more games on the schedule, freshmen team that played intercollegiately, questions about the eligibility of players, and the use of the Notre Dame shift that put up to 4 players in motion at the snap). In particular:
So Maisel did a good job capturing the feud, but washes over the validity of Yost's concerns about Notre Dame's 1909 and 1910 teams.
LSA '89 - MBB Natl Champions, Big 10/Rose Bowl Champions | @MGoShoe