Throwing a hard fastball and then backing it up with a hard slider can be one of the most dangerous combinations any pitcher can have especially if their fastball has any run on the pitch. Scouting a slider consists mainly of looking for the late action on the pitch and the velocity that is used on the slider.
A slider should sit velocity wise in between the fastball and curveball. A slider will be thrown just like a fastball all the way up until the release point, in which a pitcher will then slightly break his hand and slide the ball out.
When scouting a slider the first think to take a look at would be similar to every pitch thrown and that is to watch the velocity on this pitch. Once velocity is charted watch the arm action, is the pitcher showing he is throwing a slider at all or does it look similar to a fastball?
Much like a curveball you want to see how great of a movement and cut the pitch has when thrown. A really solid slider from a RHP will cut far outside and as late as possible, making it near impossible for a batter to hit.
Most often a slider is not very effective with soft throwing pitchers, as this pitch normally needs a higher level of velocity to get true cut on it. Watching a pitcher, try and catch how different his slider and curveball are if he throws both of these pitches. Does his fastball have any run to the inner part of the plate making his slider towards the outside of the plate that much more effective?
One other part of a slider is looking at the different planes the pitch takes when it is thrown. A one plane slider can be less effective as it comes across the plate there isn’t any downward action that takes place. A 2 plane slider will come across the plate hard and break down towards the dirt as the pitch is crossing home. A 2 plane slider can be put into the conversation of one of the hardest pitches to hit.
When is this pitch being thrown in pitch counts? Is the pitcher confident throwing this pitch or does his slider get hit pretty easily?
All these questions must be asked when scouting a pitcher’s slider. I like to watch velocity and arm action the most for this pitch. A pitcher needs to throw this pitch just as if its a fastball up until he lets the ball go.
Drew Storen on the Washington Nationals has one of the best sliders in the game. When watching Storen his fastball at times can run up and in on a batter and then he will throw his slider low and away with a great deal of cut.