I like American football. I personally only follow the NFL, and do not watch college football generally. My interest in the sport is a bit eccentric. I don't watch games live for example, I watch them after the fact where I can rewind or fast forward where I like and there are no commercials. I don't root for teams, I just like to see the games and plays. The teams I would be closest to fans of would be the Denver Broncos and Jacksonville Jaguars, but I don't have team loyalties. The Broncos have been pretty good since they got Peyton Manning but I didn't like watching them so I didn't much.
I don't really care who wins or loses. The teams I follow most are whatever teams run a particular type of "zone blocking" system(although there's more to the offense that I like than just a particular implementation of a run blocking system) brought into the league by
Mike Shanahan and
Alex Gibbs in the 1990 with the Denver Broncos. So currently that would make me a follower of the Denver Broncos(head coach Gary Kubiak was the offensive coordinator of those old 90s Broncos teams, also Rick Dennison was another coach on those teams) and the Atlanta Falcons(Mike Shanahan's son is the offensive coordinator, and he runs the same system). I would also say that I'm kind of a fan of Mike Shanahan himself, but he's out of the league and so is Alex Gibbs. Secondarily I might follow some other team who has a system that I am interested in, but I'm not really a "fan" of any team.
I do like football quite a bit though. I have always found it fun to play, but later in life I have developed a fascination with formations, plays, techniques, matchups, and strategies of the game. My interest in the game is narrowly focused. I have gotten to the point where most of the time I only watch teams that fit the criteria I described above, and I do not even watch whole games. I just watch the offense of the zone blocking teams. I like to watch the execution of the plays, what the defense tries to do to stop them, try to imagine variations of plays, and in a casual, amateurish sort of way to study the offense and how it is defended. Sometimes I'll watch another game if something else fascinates me, but the point is, I like to watch football for strictly nerdy reasons, and my main interests can be pretty narrow.
I also like to read about football(where my interests run in the same nerdy direction but they're less focused on a particular system), I spend a lot of time following various news, breakdowns of plays and such. I have looked at playbooks, watched coaching clinics, etc. There are for
example youtube videos(language NSFW) of Alex Gibbs talking that I've watched so many times over.
And of course sometimes it's fun to play imaginary coach or general manager or whatever in one's head and try to imagine what one would do differently. For me football is kind of a fun hobby to learn about and think about, rather than something where I am emotionally invested in one team beating another. I don't pretend I have zero preferences, but which teams wins and loses, and the drama and excitement of all that is not what I watch for. TBH if simulation football games weren't such garbage I might watch less football and satisfy my interests more with playing games. But as things are, only watching the game played at the highest level satisfies my interests because football video games are too primitive and poorly designed.