Ed Lopat repeatedly emphasized that you don’t mess with a pitcher’s arm slot unless he’s really screwing up. The best way to determine what a pitcher’s natural arm slot, arm angle, whatever you want to call it, is just watch him (or her) in the process of throwing a bullpen session and then take it from there. When he was showing me how to throw a good slider, he watched me as I was familiarizing myself with the pitch, and the first thing he noticed was that I was a true, natural, honest-to-gosh sidearmer with a consistent release point, and he said to himself, okay, that’s what we’ll work with.