What Does Your Throwing Arm Do During The Pitching Delivery?
Most instructors and coaches will say that you cannot change a player's arm action during their throwing motion. For the most part, this is true, but I have had success changing one particular action in the throwing motion to add velocity to any thrower.
When a pitcher starts their delivery and their throwing hand breaks from their glove, we want to have there and facing the ground. As their arm starts to move up we want them to pull their elbow back towards first base if they are a right-handed thrower and third base for a left-handed thrower. This allows for their arm to get in a cocked position and allows their arm to move faster during the throwing motion.