John A. Slagle (November 1869 – February 19, 1915) was an American pitcher in Major League Baseball.

He pitched one game, 11⁄3 scoreless innings, being credited with a save, for the Cincinnati Kelly's Killers of the American Association on April 30, 1891.

After his brief major league appearance, Slagle pitched through 1896 in the minor leagues.

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