Re: SI joint pain.
Exactly as that article describes - the SI joint is really where your torso meets you lower body. Often times SI pain can be called "sciatic pain" and there is some overlap.
PT and rest can be the most helpful, as long as other things are being ruled out (like insufficiency fractures, or other injury to bone/muscles, and disk injury to the lower back).
So hopefully Adamczewski can get some rest, PT and get back to swinging soon. Good luck Josh.