In baseball, a submarine pitch is one in which the ball is released underhand and just above the ground, with the torso bent at a right angle and shoulders tilted so severely that they rotate around a nearly horizontal axis. (This is in stark contrast to an underhand pitch in softball in which the torso remains upright, the shoulders are level, and the hips do not rotate.)
The "upside down" release of the submariner causes balls to move differently than pitches generated by other arm slots. Gravity plays a significant role, for the submariner’s ball must be thrown considerably above the strike zone, after which it drops rapidly back through. The sinking motion of the submariner’s fastball is enhanced by forward rotation, in contradistinction to the overhand pitcher’s hopping backspin.
Submarine pitches are often the toughest for same-side batters to hit (i.e., a right-handed submarine pitcher is the more difficult for a right-handed to hit, and likewise for left-handed pitchers and batters). This is because the submariner’s spin is not perfectly level; the ball rotates forward and toward the pitching arm side, jamming same-sided hitters at the last moment, even as the ball drops rapidly through the zone.
The rarity of submarine pitchers is almost certainly attributable to its unusual technique. It is not typically a natural style of throwing—it is often a learned style—and because the vast majority of pitchers use an overarm motion, most young pitchers are encouraged to throw overhand.
Though the bending motion required to pitch effectively as a submariner means that submariners may be more at risk of developing back problems, it is commonly thought that the submarine motion is less injurious to the elbow and shoulder.
Past major league submariners include Carl Mays (whose unorthodox delivery possibly contributed to the fatal beaning of Ray Chapman), Ted Abernathy, Elden Auker, Chad Bradford, Mark Eichhorn, Kent Tekulve and Dan Quisenberry.
Shunsuke Watanabe of the Chiba Lotte Marines is known as "Mr. Submarine" in Japan. Watanabe has an even lower release point than the typical submarine pitcher, dropping his pivot knee so low that it scrapes the ground. He now wears a pad under his uniform to not injure his knee. In addition, his release is so low that his knuckles often become raw from their periodic drag on the ground.
Present day submarine/sidearm pitchers 
- D. J. Carrasco
- Randy Choate of the St. Louis Cardinals
- Chong Tae-Hyon of the Lotte Giants
- Daniel Davidson of the Los Angeles Angels of Anaheim
- Joey Devine of the Free Agent
- Pedro Feliciano of the New York Mets
- Brian Fuentes (Retired)
- Cory Gearrin of the Atlanta Braves
- Sean Green of the Texas Rangers
- Kim Byung-Hyun of the Nexen Heroes
- Mike Koplove of the San Diego Padres
- Javier López of the San Francisco Giants
- Kazuhisa Makita of the Saitama Seibu Lions
- Jay Marshall is a Free Agent
- Cla Meredith is a Free Agent
- Peter Moylan of the Los Angeles Dodgers
- Pat Neshek of the Oakland Athletics
- Darren O'Day of the Baltimore Orioles
- Dan Quisenberry of the Kansas City Royals
- Clay Rapada of the New York Yankees
- Chris Schroder of the Miami Marlins
- Joe Smith of the Cleveland Indians
- Mitch Stetter of the Los Angeles Angels
- Yoshinori Tateyama of the Texas Rangers
- Joe Thatcher of the San Diego Padres
- Ehren Wassermann of the Long Island Ducks
- Shunsuke Watanabe of the Chiba Lotte Marines
- Brad Ziegler of the Arizona Diamondbacks