This video shows how to throw a sinker baseball pitch. The instructor begins by showing his two seam grip on the ball and notes then he does not use the strong thumb tactic while pitching. The instructor explains how he throws through the inside of the baseball which involved his hand rolling over mid way through the pitch. Another pitching technique the instructor shows is the cross finger throw which is when you hold the ball securely with only two fingers on the ball with the thumb only slightly secured below the ball. The instructor notes that using a stiff thumb is used quite commonly amongst pitchers but he does not incorporate stuff thumb into his pitching style.
Have an iPhone? Check out all 200+ new features coming in iOS 13.