The Oakland Athletics‘ biggest rival is the San Francisco Giants. This rivalry comes as a result of The Bay Bridge Series championship.

The Bay Bridge Series refers to the games between the Oakland Athletics of the American League and the San Francisco Giants of the National League, as well as their rivalry. The San Francisco–Oakland Bay Bridge, which connects the cities of Oakland and San Francisco, is the inspiration for the series.

Unlike Cubs-White Sox or Mets–Yankees games, when hatred runs rampant, the regional rivalry between the A’s and Giants is regarded as a cordial one with the generally mutual friendship between the supporters. While many supporters have a deep disdain for the other side, others have a soft spot for both. On this subject, baseball fans in the Bay Area tend to differ.

The Bay Area Rapid Transit system that connects Oakland and San Francisco is also referred to as the “BART Series.” However, outside of a tiny number of history books and national broadcasters, the moniker “BART Series” has never been popular and has gone out of favor. The rivalry is almost entirely referred to as the “Bay Bridge Series” among Bay Area residents.

Originally, the phrase referred to a series of exhibition games between the two clubs following the completion of spring training and just before the regular season began. It was initially used to allude to the 1989 World Series, in which the Athletics won their most recent championship and the first meeting between the two clubs since their relocation to the San Francisco Bay Area. Since the start of interleague play in 1997, it has also referred to games played between teams during the regular season. The A’s have won 53 games so far this season, while the Giants have won 50.