- lace (1887)
- late-inning defensive replacement (1949)
- late-inning pressure (1935)
- late-season pickup (1940)
- lay down (a bunt) (1898)
- lay off (1916)
- lazy hit (1887)
- lead off (1865)
- leadoff batter / leadoff hitter / leadoff man (1896)
- lead runner (1902)
- learn the batter / learn the hitter (1888)
- leave the bench swinging (1937)
- leave the yard (1977)
- left fielder (1862)
- leg out (1907)
- letter high (1910)
- let the ball play him (1908)
- level swing (1908)
- light-hitting (1891)
- line drive (1876)
- line drive to the catcher (1908)
- line hit (1870)
- line hitter (1891)
- line hugger (1910)
- liner (1867)
- line up (1891)
- lineup card (1914)
- long relief (1932)
- long reliever (1950)
- Lord Charles (2009)
- lose a step (1917)
- loss column (1901)
- loud foul (1888)
- Lou Gehrig’s Disease (1939)
- low-ball hitter (1887)
- luck out (1902)
