Who's asking: Rebekah Giannini, Richmond, VA
As Rebekah notes, the Red Sox are not the only team whose fans sing this song, but the song has become associated with them, in particular. The movie "Fever Pitch" showed Fenway Park fans singing along, and we minor-league fans at Hadlock Field sing it, too.
The "Sweet Caroline" phenomenon is a good example of how new customs can be created so quickly that no one even remembers a time before they existed. "Sweet Caroline" has only been a staple at Fenway Park since 1998, when the stadium's music director, Amy Tobey, started to play it at random times between the seventh and ninth innings -- but only when the Sox were ahead. In 2002, the team's new management asked her to play it every game, in the eighth inning. It's been an official tradition ever since.
What's great about "Sweet Caroline" is that everyone can sing along even if they don't know the words; the words are dumb, but even so, everyone can sing "Ba ba BA!" between the lines of the chorus.
I don't really care about this year's World Series. Many, many years ago, I rooted for the Detroit Tigers because my then-boyfriend did, and I rooted for the Mets because the Tidewater Tides (as they were then known) were the Mets' AAA affiliate. But now the Orioles have acquired the Norfolk Tides, and I haven't heard from that old boyfriend in a very long time, so I have no stake in these games. Bring on college basketball.