One of the bits of wisdom I have picked up over the years is the truth of the saying "
incompetence is more common than conspiracy". I can see that this might be the case here.
I would suggest that you document the bruising with photographs (like the one you have shown us), and take them along to the Sensei. I suspect (hope) that he/she will be every bit as appalled as the rest of us.
If your lad is a tough little cookie (and I suspect he is) then he won't have made much of a fuss while this was going on, and the Sensei may have absolutely no idea of how much contact was really being delivered. Incompetent - absolutely. Deliberate - I doubt it, but I accept I could be wrong.
Above all, don't just do nothing. Otherwise, nothing will change.
