My initial reaction, both as a teacher and as a mum of a dd whose learning has been disrupted by defiant pupils, was to feel some sympathy for the teacher and to wonder what your son had done that led to him being shouted at.
But your update reminded me of your previous thread.
I think that there's a world of difference between a disruptive pupil who affects the learning of others and a basically good kid who is generally well behaved but finds contact sports intimidating.
I was rubbish at P.E., hated it at secondary school and - even though I left 35 years ago still have horrible vivid memories of it. Hockey incurred the risk of being shouted at by the talented competitive girls and being hit on the shins by hockey sticks. I soon learned to run up and down the edge of the pitch keeping well away from the ball. Cricket could also lead to being shouted at by "team mates" if you missed a catch or dropped a ball. When fielding, I worked at which angle the ball was unlikely to be hit so that I knew where to stand to keep out of the ball's way.
I think that your son needs to try develop similar tactics to get through the remaining ruby lessons (hopefully there aren't too many left). He needs to make sure that he's getting changed, looking busy and active but avoiding contact as much as possible.
I do know that there are lots of issues with school-boy rugby, but it's really unlikely he will get injured in PE lessons.
Actually, the OP's previous thread attracted comments by posters with rugby experience who said that there are risks, particularly for a nervous child.