William Ellsworth Blair (September 17, 1863 – February 22, 1890) was a Major League Baseball player. A left-handed pitcher who batted from the left side, Blair had a listed playing weight of 172 pounds. Blair had signed a contract to spend the 1890 season with the Chicago Cubs, but he died as a result of illness before games began, during the first outbreak of the 1889–1890 pandemic. His obituary listed the cause of death as "influenza, which turned into pneumonia and typhoid fever".