In order to progress to more complex shoulder loading its important build a solid base.  Here are a few simple scapular loading and shoulder stability exercises that can be made more challenging and once mastered will help with the performance heavier and more dynamic overhead activities.  These exercises are part of a larger arm care routine I have my overhead athletes perform after the manual tissue and joint prep, and prior to a full body movement prep.

These can be easily replicated out on the field using the dugout bench.