Your son was the only one not in the lineup. Do they only have ten players?
How does he play great in the next game without getting in the lineup?
Has anyone other than your son told you the coach told him he needed to hit better to play in front of the team?
He doesn't get invited to a camp then he gets in the lineup and plays poorly?
Your son's skills gets blamed for the team losing by ten runs in a game he didn't play?
Does your son have trouble receiving pitches?
I was a starting pitcher from LL through high school. I never asked who is my starting catcher. I only asked who will warm me up.
No one else had to earn their starting spot?
These are my questions. I have to admit your post is a little beyond comprehension. It's also a little beyond believable. I had some real in your face coaches back in the day when it was acceptable. I never saw anything like this. This kind of behavior would get a coach fired today. Are you sure your son isn't underperforming and making up stories?
If these things are actually occurring document them. Then go past to the coach to the AD and principal. Accuse the coach of emotional abuse and humiliation.
I believe somehow truth and reality aren't meeting at the same intersection.