Who really knows? I do know this. The players coaches see potential in they will push. The players coaches feel are not working hard enough, motivated enough, tough enough, focused enough, who they see true potential in will spend energy on those players. We can argue on how that energy should be spent.
But regardless what does a player do when they "feel" they are the subject of negative energy? What does a player do when they "feel" they are being singled out in a negative way? Do they fall into the trap of becoming negative themselves? Do they simply dry up and wilt under the "pressure?" Or do they take it as a challenge and work even harder? Do they go out to prove the coach is wrong about them? Or maybe they will end up proving that the coach is right about them?
There are numerous scenarios that play out in these type of situations. The player feels he is being singled out. Other players who are unhappy with their situation feed into this and convince the player he is being screwed. The player tells Mom and Dad and they feed into this. The player becomes negative the parents become negative. The player is convinced he is being targeted and so do the parents. The player ends up with a miserable experience and of course so do the parents. Or the player takes this as a challenge to prove himself. He works even harder. He decides he is not going to fail. He takes each negative comment as a personal challenge. He is determined to overcome and succeed. The parents feed into this mentality and encourage the player to keep on pushing.
There were times I called out players in front of the team. I never called out a scrub in front of the team. I never called out a scrub period. What's the point of doing that? Why would you bring any negative energy to the table and waste any energy on a player you saw no potential in? Wouldn't it make more sense to spend your energy on the players you felt needed it in order to reach their potential you actually believed they had?
Again we can argue about how to motivate. How you shouldn't motivate. We can argue about tactics and ways you should and shouldn't push players. But who pushes players buttons that are not in your mind worth pushing? OP I would focus on what my son was doing to get better. I would focus on him blocking everything. Throwing better. Receiving better. Hitting better. Working harder than anyone else. I would be so good the coach would look like a clown for ever saying anything negative about me. It's not good enough to say he does things as good as the other kids. Maybe the coach expects more out of your son and when he doesn't get it he isn't shy about saying it?
I don' t know. What is your son going to do about it? Come home and lay his head on your shoulder and tell you how the coach is picking on him? Or is he going to go to work and shove it in the coaches face? And then he can one day thank this coach for motivating him to become the player he has become. He can still think the coach is a total piece of garbage. That's fine. He might be. But what has that got to do with your son's desire to be the best he can be? Choices OP. Your son has choices. And so do you.
Here is the deal imo. You can't control the coach. Who the coach is. How he decides to coach. What do you control? Well then control it. Look the coach in the eye with sweat pouring off your face and a dirty uniform and when he lays into the team stare him right in the eye. Know you put in the work. Know you just put all you had into it. Know that you are working as hard as you possibly can and let him know that no matter what he says, no matter what he does, you will not break me. I will not go away. I will not wilt. I will not fade. I will not be denied. I AINT GOIN NOWHERE.
I don't know about this coach. He might be a total clown who enjoys picking on players. And? That has what do with your son's desire to be the absolute best player he can possibly be? Unless he becomes the excuse your looking for. Instead of seeing this as a reason to fail use it as one of the reason you will refuse to fail. Good Luck