- across the letters (1903)
- aggressive hitter (1898)
- all-important loss column (1935)
- All-Star break (1947)
- anybody’s game (1864)
- appeal play (1921)
- aspirin (1939)
- attendance bonus/attendance clause (1934)
- autographed ball (1909)
- automatic out (1929)
- automatic strike (1932)
