This got me thinking at what the biggest splits would be for "one-sport fandom" schools (obviously not accounting for LITERAL "one-sport" schools ... obviously there are no Marquette football fans, lol).
1. Notre Dame probably takes the cake ... legions of bandwagoners across the nation for its football program, and I'd wager less than 5% of them consider themselves Notre Dame basketball fans.
2. Duke basketball vs. Duke football has got to be one of the more dramatic drop-offs out there. I wouldn't be surprised if it approaches the Notre Dame situation in reverse on a ratio basis.
3. Penn State football to basketball seems like a colossal drop-off. While PSU football doesn't have the national (and I would say "random") appeal of Notre Dame or Alabama or whatever, it seems like within Pennsylvania and the surrounding regions, you have a ton of people who might be, say, PSU football and Villanova basketball fans.
4. Alabama, as discussed. However, while their bandwagon fans across the nation probably pick a random basketball Blue Blood to cheer for, I think within the state of Alabama it's more a question of passion. In other words, I think most local Alabama football fans are "Alabama basketball fans" ... it's more an issue of not really caring.
For other schools like Ohio State football, Michigan football, Kentucky basketball, etc. where one sport seems like a much bigger brand, I think it's often more of an issue closer to #4 than the three above that. I think a lot of OSU or Michigan football fans don't necessarily have a separate favorite basketball program ... they just don't engage with the basketball side of things nearly as much. Would love to hear anecdotal cringe examples of the reversible jacket phenomenon from others who live across the nation! I even once heard a friend who lives in Pasadena say that there are a lot of casuals out there who cheer for USC football and UCLA basketball ... something any self-respecting person would find utterly embarrassing.