Bay Bridge Series

The Bay Bridge Series, or the Battle of the Bay, is a series of baseball games played between—and the rivalry of—Major League Baseball's Oakland Athletics of the American League and San Francisco Giants of the National League. The series takes its name from the San Francisco–Oakland Bay Bridge which links the cities of Oakland and San Francisco. As of 2018, the winner of the annual series retains a trophy fashioned from a piece of the original bridge.

Although competitive, the regional rivalry between the A's and Giants is considered a friendly one with mostly mutual companionship between the fans, as opposed to Cubs–White Sox, or Mets–Yankees games where animosity runs high, though sections of each fanbase does harbor towards the entirety of the other. This, however, is limited as many people see the opposing team as no threat to their own; hats displaying both teams on the cap are sold from vendors at the games, and once in a while the teams both dress in uniforms from a historic era of their franchises. Many fans actively cheer for both teams when they are not playing against the other. A's fans cite the Giants blocking a potential move to San Jose as a point of contention.

The series is also occasionally referred to as the "BART Series" for the Bay Area Rapid Transit system that links Oakland to San Francisco. However, the name "BART Series" has never been popular beyond a small selection of history books and national broadcasters and has fallen out of favor, likely because BART does not provide direct or easy access to Oracle Park in San Francisco. Bay Area locals almost exclusively refer to the rivalry as the "Bay Bridge Series" or the "Battle of the Bay."

Originally, the term described a series of exhibition games played between the two clubs after the conclusion of spring training, immediately prior to the start of the regular season. It was first used to refer to the 1989 World Series which the Athletics won and the first time both teams had met since they moved to the San Francisco Bay Area. Today, it also refers to games played between the teams during the regular season since the commencement of Interleague play in 1997. Through the 2023 season, the A's have won 74 games, and the Giants have won 70.