Prior to his pitching sessions, what does he do to prepare? He looks rather stiff in the shoulders and his lower body does not compliment his upper body.
How can I tell that his lower body is acting independently? Watch his stride foot upon lading, then watch that foot as his finishes his release. It lands off center to his pitch direction, then quickly slides/shuffles off to his right. I would suggest reasons and other things to correct that, but for right now he should address that discomfort and pain in his elbow.
My suggestion would be to shut down for 2 weeks, apply warm compresses to the area of concern, when he comes home from school every two hours, and continue that application over the weekends. Also, after each warm compress (towel), rub with a liniment like Absorbine Jr. Then, start with another warm compress (towel) and repeat with liniment, and give the arm a rest. To continue with the issue of discomfort by using a compression wrap - like in the video ,is not helping the matter.
After a 2 week period, do a light set of reps with a 2 lb. weight only - bicep curls and triceps pushes. If your son still encounters the same issues with his elbow, its time to call in the medical professional.
If he doesn't have elbow issues after his 2 week shutdown, that pitching coach in the video should be conducting a "preseason" conditioning program that gets your son in the swing of things for the season.
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