Delayed Arm Rotation
Why maintain the same arm speed every pitch? The rulebook states after you begin your forward rotation, you may NOT stop nor reverse your arm circle. But it's totally LEGAL to vary the speed of your arm circle.
Starting normal speed, drop your arm back and come up quickly even with your belly button. Slow your arm down to a crawl keeping it moving slowly for two seconds until it's above your head.
Keep your feet still or just lift your left leg without pushing off yet. From 12 o'clock on, speed your arm back up to full speed to push off with your legs.
After you show it with a fastball, do it with a change up and they won't know what's happening!