Shoulder dipping solution?

No idea if this is Zach's problem without a video, but my boy played with a kid who started dipping his back shoulder when he switched to big barrels. The problem ended up being two-fold. First, he was standing to erect. No bend in the back knee, he was compensating by dipping his shoulder. Second,he was dipping his back shoulder instead of bending at the waist, especially for the low and away pitch.

Hope that helps some.

Without seeing a video it's tough, but just for kicks check his grip. You mentioned that he just went to a big barrel bat, which is slightly heavier in most cases. Check to see that he still has his top hand on the bat properly. What I mean is make sure that his top hand/wrist is still cocked/cupped. I have seen kids compensate for the additional weight by straightening the top wrist which can cause their shoulder to drop during the rotation of the swing. Just something to check... You'd be surprised at how important a proper grip and setup is... and how easily it can be disturbed by a couple of ounces.

R.