Over here in the UK and also in Europe I would say theirs a lot of rivalries within football (soccer) that would out do the rivalries listed there. I'm from Newcastle and a Newcastle United fan, so for me the Tyne and Wear Derby is a big one for me. People have mentioned tha Old firm Derby, theirs a whole list in the UK that are massive, in Europe theirs some big ones as well. The Classico, Barcelona vs Real Madrid is massive, so too would be Benfica vs Sporting Lisbon, and Fenerbache vs Galatasaray.
The focus on American rivalries are daft, over there the distances between cities means that for the most part you won't come across many other fans in day to day life. Not only that but your seasons are short and people tend to be fans of more than one sport, meaning people invest less emotions than those who literally live or die by their team (not saying you don't have you fair share of fans like that though). On top of this with cities elsewhere in the world being closer and in a lot of cases multiple teams in the same sport in the same city then theirs a lot more at risk for fans of teams over here. Some rivalries also go beyond the sport, the old from Derby is a big example of this, the same for the Classico, and you could also say the same for Oxford and Cambridge in the boat race.
Good points.
But there are many fans here who most follow one sport.
I don't do hockey that much and like football, baseball, and basketball, so I like three sports but would be thrilled if San Jose won in hockey. I am split but not all are.
But so many dedicated sports fans I know like primarily football and baseball, but there are still many who only follow just one or the other. And I would say there are millions of fans of four sports, millions including me who follow three sports, the biggest amount imho following two sports, and still millions who follow just one sport so it's not as if sports in general aren't getting attention around any small or large neighborhood in the USA.
I won't even make the ridiculous assumption that there is a sport in the USA as big as soccer in the UK or the world since I lived in London as a student and have seen the loyalty it can bring.
But I would also safely say that baseball here is more popular than the other three American major sports combined for several reasons. The other three are big sports but baseball is religion. It's a long season and preseason and there are 162 regular season games in the sport so many can see most teams nearby. Also there's a personal history of baseball players that are larger than life whether it's a person like Pete Rose who long was compared to the American worker just plugging away, or Joe DiMaggio who married the most famous celebrity of the time, Marilyn Monroe, yet was just as famous himself being a key player for the top team, the New York Yankees. And even larger than life players born in other countries come here and make giant names beyond just the sport like Ichiro. Baseball spurns heros so big that even non-baseball fans know the names. Before I followed baseball, I already heard many of the names. Like I said, baseball is religion. You don't have to worship but will still be familiar with the names. It's like you can be an atheist but will know the names of Moses, Jesus, Mary, Peter, Paul, etc.
I know that soccer is more than sport and it's a religion, but baseball over here is also a religion. Your religion has billions of followers, yes, but baseball would still have 100 million huge fans between just here, Japan, Mexico, and Central America.