Here's another baseball pitching tip...
Why is flexibility training important?
Pitching is a rotational activity, the hips and core are chief couplers of power to the arm.
As the stride foot lands, the internal rotators of the hips along with the core rotate the midsection to face the plate.
If the external rotators are tight and don't stretch to their full normal ROM (range of motion), the whole kinetic sequence is impeded.
Good flexibility leads to better velocity.
Work on it!