Fan culture in general is so different in US sports to the UK, specifically, football culture.
I went to an Oakland Raiders with a few American mates and they spend weeks telling me how intense it was, how scary "the black hole" at The Coliseum is, how I'd be terrified etc. I reassured them that I'd been in Rome with The Carabinieri following us around, I'd been teargassed in Zurich or chased around Moss Side by Man City and I reckoned it would be fine. So I went to the game, and I'm not lying when I say I'd been to more intense and scary pre-season friendlies (Hull away for one). Everyone from both sides having a great time, some light hearted banter and some people dressed as Hellraiser were as scary as it got. They wouldn't have it that this wasn't the most intense thing I'd ever seen.
I've also been to 49'ers games where the 1st day of a test match looked like Boca V's River Plate in comparison.
From a soccer / football perspective I took myself off to Reno for the weekend, and took in a game between Reno1868 & Tulsa Roughnecks, in the USL Championship (the division below MLS). Ignoring that the standard of football was dreadful, what got me was:-
1) Their equivalent of Roary the Lion was dropped off in a helicopter 5 minutes before the start of the game into the centre circle
2) The stadium announcer was work than Mark Page, and announced corners with all the enthusiasm of a last minute winner in a FA cup final
3) The fans spent most of the game with their backs to the pitch as they focused on their choreographed singing and dancing, and when Reno scored it was almost an irrelevance that got in their way of the 3rd verse of the chant they were on at the time.
I love the US, and love baseball, but other than that American sports, and the lack of fan culture, leave me cold.