| Jack Theis | |
| Position: | Pitcher |
| Bats: | Right |
| Throws: | Right |
| Birth Date: | 23 July 1891 |
| Birth Place: | Georgetown, Ohio |
| Death Place: | Georgetown, Ohio |
| Debutleague: | MLB |
| Debutdate: | July 5 |
| Debutyear: | 1920 |
| Debutteam: | Cincinnati Reds |
| Finalleague: | MLB |
| Finaldate: | July 5 |
| Finalyear: | 1920 |
| Finalteam: | Cincinnati Reds |
| Statleague: | MLB |
| Stat1label: | Games played |
| Stat1value: | 1 |
| Stat2label: | Innings pitched |
| Stat2value: | 2 |
| Stat3label: | Earned runs |
| Stat3value: | 0 |
| Teams: | |
John Louis Theis (July 23, 1891 – July 6, 1941) was a pitcher in Major League Baseball. He played for the Cincinnati Reds. Theis holds the record shared by many for the lowest ERA in MLB history, having not allowed an earned run in the only game of his career.[1]
He died from a heart attack in 1941 shortly before his 50th birthday.