Jim T, I applaud you on your intervention! And personally I don’t care who it was in front of because that wasn’t on you, it was on the coach who made a very poor decision.
The problem is the coach holds the cards to the player's future. I've seen coaches take it out on players when the parent showed them up publicly. Get pissed and leave the program? Sure. It means sitting out a year. To approach the coach is in the best interest of the kid. To "confront" the coach in front of others is not wise. And regardless of the subject It's not very mature and level headed.
OP: Keep in mind the poster who told says you did the right thing has never coached at any level. He has no experience on how a coach feels to get showed up in front of his team and parents. He has no idea how the coach holds the power card in these confrontations.
I agree with those who say a plan for how he would be used in his comeback from surgery should have been developed before the season. When he hits pitch X he's out of the game.