- I got it (1889)
- infield fly rule (1894)
- infield hit (1870)
- inherited runner (1926/1947)
- innings eater (1978)
- inside-out swing (1960)
- inside-the-park home run (1900)
- inside corner (1888)
- insurance run (1934)
- Iron Mike (1942)
- issue (a walk) (1897)
Earliest uses of baseball terms