When you think of rivalries, often a few big ones probably come to mind—Yankees/Red Sox, Dodgers/Giants, Michigan/Ohio State, Broncos/Raiders, and the list goes on. Thomas Harding of MLB.com told me that rivalries in professional sports usually come about for one of two reasons—either because two teams are playing well together at the same time or they are going through very similar circumstances at the same time, since there aren’t a lot of geographical rivals within their divisions in most cases.
He cited the Cincinnati Reds and Los Angeles Dodgers when both were World Series contenders in the NL West (sound familiar?