Good morning, sidearmboy, and I just want to say that we're talking about one of the deadliest pitches one can have in the repertoire. The sidearm slider was my strikeout pitch for more than 20 years, and I will be happy to tell you about it. The grip is the standard one which I learned from Yankee ace Ed Lopat many moons ago, and it's just this: very much offcenter, index and middle fingers very close together and the middle finger just touching one seam, thumb underneath for support and resting on a seam, the fourth and fifth fingers sort of curled up on the outside of the ball. I remember, as vividly as if it were yesterday, how Lopat told me "Throw it like a curve, but roll your wrist, don't snap it"---think of a chef flipping a pancake or a crepe. The slider can be a power pitch---a hard one, which I used---or it can be used as a changeup, depending on how firmly or how loosely you hold the ball. AND---since you're a sidearmer, like me, you can add the crossfire move to your delivery which will make that pitch virtually unhittable! Again, Ed Lopat: he told me that the crossfire will work with any pitch, even that obstreperous knuckleball, so if you're thinking of other pitches, yes, you can throw them sidearm and use that crossfire. Remember this---you have to throw every pitch with the same arm motion and the same arm speed because you do NOT want to telegraph those pitches.
Oh. How to do that crossfire: you go into the windup, or the stretch, or even that no-windup motion Don Larsen used when he pitched his perfect game---but instead of going directly to the plate, you take a step toward third base (again, for a righthander), whip around with your whole body and fire the ball to the plate from that angle. The batter thinks it's coming at him from third base---or from behind the pitcher's back---and he gets so confused and discombooberated that he ends up striking out, again and again! I recall how I used to lose track of my strikeouts because I kept piling them up!
And there you have it. Any more questions, ask away, and I'll be glad to answer them.
Goddess of the Slider (sidearm of course)