From BR Bullpen
In baseball, the palmball pitch is a type of changeup. It requires placing the baseball tightly in the palm and then throwing it as if throwing a fastball. This takes some of the velocity off the pitch, intending to make the batter swing before the ball reaches the plate.
Notable pitchers who have been known to throw the palmball include Steve Farr, Edwar Ramirez, Dave Giusti, Bob Stanley, Roy Halladay, Orlando Hernández, reliever Tony Fiore, "changeup" pitcher Trevor Hoffman, and 1990s reliever Joe Boever.
 Slip pitch
The slip pitch was a similar pitch taught by Paul Richards to many young pitchers throughout Richards' career. As it is very similar to the palmball, slip pitch and palmball are often used interchangeably.