| John Slagle | |
| Position: | Pitcher |
| Bats: | Left |
| Throws: | Right |
| Birth Date: | November 1869 |
| Birth Place: | Lawrence, Indiana |
| Death Place: | Indianapolis, Indiana |
| Debutleague: | MLB |
| Debutdate: | April 30 |
| Debutyear: | 1891 |
| Debutteam: | Cincinnati Kelly's Killers |
| Finalleague: | MLB |
| Finaldate: | April 30 |
| Finalyear: | 1891 |
| Finalteam: | Cincinnati Kelly's Killers |
| Statleague: | MLB |
| Stat1label: | Win–loss record |
| Stat1value: | 0–0 |
| Stat2label: | Earned run average |
| Stat2value: | 0.00 |
| Stat3label: | Strikeouts |
| Stat3value: | 1 |
| Teams: | |
John A. Slagle (November 1869 – February 19, 1915) was an American pitcher in Major League Baseball. He pitched one game, 1 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.