[header] How to throw a great two seam fastball [title] Place your index finger and middle finger on the seams. [step] Find the part of the seams where the gap between them is narrowest. Lay each finger so it runs parallel with one of the seams. 
The horseshoe shape of the seams should be opened upward. [substeps] Experiment with your fingers resting just inside the seams as opposed to directly on top of them.