- Backstop (Catcher) (1866)
- Backstop (Screen) (1868)
- Bad-Ball Hitter (1913)
- Bad Hop (1906)
- Ball Hawk (1908)
- Ballpark Figure (1957)
- Balls and Strikes (1866)
- Baltimore Chop (1897)
- Bandbox (1894)
- Bang-Bang Play (1946)
- Banjo Hitter (1929)
- Baseball Age (1889)
- Baseball Cap (1865)
- baseballdom (1866)
- Baseballese (1897)
- Baseball Field (1864)
- Baseballically (1875)
- Baseballism (1867)
- Baseball Park (1867)
- Baseball Player (1856)
- Baseballwise (1900)
- Base Hit (1870)
- Base Path (1876)
- Base Runner (1865)
- Bases Crowded (1886)
- Bases Drunk (1906)
- Bases Loaded (1871)
- Base Stealer (1867)
- Basket Catch (1924)
- Batboy (1887)
- Batgirl (1916)
- Batter’s Eye (1884)
- Batter Up (1886)
- Battery (1864)
- Batterymate (1889)
- Batting (1858)
- Batting a Thousand (1954)
- Batting Average (1869)
- Batting Cage (1887)
- Batting Eye (1887)
- Batting Glove (1954)
- Batting Order (1870)
- Batting Practice (1868)
- Batting Slump (1894)
- Beat Out (1891)
- Beat the Throw (1884)
- Behind the Plate (1877)
- Beisbol (1925)
- Belly Slide (1901)
- Belt High (1901)
- Bench Clearing (1947)
- Bench Jockey (1928)
- Bench Strength (1914)
- Benchwarming – Benchwarrmer – Warm the Bench (1888)
- Big Inning (1862)
- Big League (1877)
- Big Leaguer (1886)
- Big Leagues (1884)
- Big Red Machine (1969)
- Billy Ball (1980)
- Billy Goat Curse (1950)
- Black Sox (1920)
- Bleacher (1887)
- Block the Plate (1890)
- Boo Bird (1933)
- Boston Massacre (1912)
- Box Score (1897)
- Brand New Ball Game (1922)
- Bread-and-Butter Pitch (1940)
- Breaking Ball (1907)
- Bronx Bombers (1928)
- Bronx Cheer (1921)
- Brushback Pitch (1948)
- Bullpen (1912)
- Bullpen by Committee (1983)
- Bullpen Session (1933)
- Bush League (1896)
