A term in baseball used to characterize a pitcher in baseball who consistently gets batters to hit ground balls. They are able to do this by putting a lot of downward movement on all of their pitches. This type of pitcher does not typically rely on a standard fastball, which is commonly used by strikeout pitchers. By getting the offense to hit ground balls, the pitcher keeps the ball in the infield and deprives them of scoring opportunities. Should a runner get onto base, the pitchers consistent ability to get a batter to hit a ground ball will often lead to a double, or even triple-play.
Two examples of the types of pitches ground ball pitchers use are the splitter and the sinker. Both of these pitches have spin on them which forces them to move down and away, or just down, respectively, on the ball's flight from the mound to the plate. When a batter is able to connect on either of these pitches, the ball is so low to the ground that the batter is usually unable to "pull" the ball up into the air to get it past the infield defense. Furthermore, a sinking pitch will not hit the sweet-spot of a bat, further reducing the speed of the ball as it comes off the bat.