In baseball, a sinker or sinking fastball is a type of fastball which has significant downward and horizontal movement and is known for inducing ground balls. Pitchers capable of utilizing the sinker are able to throw the pitch almost exclusively, as it forces weak contact and ground balls, allowing them to rely less on secondary pitches in order to change speeds. While coaches agree that this pitch is very similar to the two-seam fastball, a two-seamer tends to have more lateral movement than a sinker. In either case, the pitch is thrown in a two-seam orientation and has a gyro angle far from 0 degrees, leading to seam-shifted wake effects that cause downward and lateral movement compared to a four-seam fastball.
History
thumb|right|180px|[[Scott Feldman (baseball)|Scott Feldman]]
Before the 1950s, pitchers did not know what caused their pitches to sink or "hop". They regarded either ability as a "gift from heaven". Bill James cites Curt Simmons as the first pitcher to be able to throw both sinkers and rising fastballs, apparently indicating that it was not known how to make a pitch sink and how to make one hop.
Effects on the batter
The sinker drops 6 to 9 inches more than a typical four-seam fastball, which causes batters to hit ground balls more often than other fastballs, mostly due to the tilted sidespin on the ball.