In baseball, a slider is a breaking ball pitch that tails laterally and down through the batter's hitting zone; it is thrown with speed less than a fastball but greater than the pitcher's curveball.n a good slider, the dot will be down where it is not noticeable for a hitter to pick up. From the batter's perspective, this dot appears white, whereas the dot is red for a curve ball (created by the seam movement), allowing many skilled batters to immediately recognize the type of pitch.