The 2009 Yokohama BayStars season features the BayStars quest to win their first Central League title since 1998. The team made a bit of a splash just before the season, signing former Hokkaido Nippon Ham Fighters starter Ryan Glynn to shore up their rotation, led by veterans Daisuke Miura and Hayato Terahara.

On the offensive side, the 'Stars picked up Dan Johnson, a journeyman minor leaguer, to give protection to 2008 batting champion Seiichi Uchikawa and slugging third baseman Shuichi Murata.

The year did not start well even before the regular season started. The 'Stars lost Murata to a pulled hamstring muscle during the 2009 World Baseball Classic in a seeding game against Team Japan's arch-rival Korea. The injury hurt the team in the worst way, as Yokohama's bad luck with batting with runners in scoring position continued from 2008. The BayStars scored just five runs in their first six games en route to another rough start in April.

Towards the end of May, BayStars manager Akihiko Ohya announced that he was taking a sabbatical, which turned into his resignation. Ohya's sudden resignation ended his second tenure as Yokohama manager. He had been manager previously from 1996 to 1997 and helped to put together the 1998 Japan Series Championship team. Ni-gun manager Tomio Tashiro was called on to replace Ohya, and he seemed to be the logical choice since he had been successful managing the ni-gun Shonan SeaRex. However, Tashiro could not turn the team's fortunes around as the team stumbled to another last-place finish in the Central League.