My wife is an Iowa graduate. I consider her a Hawk fan. She wants them to win. She usually knows one or two players, at most. But we have Iowa State football season tickets, she knows Iowa State players and wears lots of ISU clothing, and not just to games. Also, her son, my stepson, is a huge Husker fan. So we cheer for them too, although I see their teams, coaches, fan base and Athletic Department without the blinders on that plague so many of them.
But I guess as far as the original question, I think a fan can be anyone with any level of interest or knowledge. Just wanting a team to win is enough.