The hardest thing a loving, baseball parent will ever have to do .. is what you NEED to do here! Be there to support him, make sure he understands both sides of this consideration ....... then tell him" that it's his decision and you will support him either way!"
If you push, he will likely stop for sure! It's kind of like telling your daughter you "can't stand her boyfriend." She's sure to hang on then. Stay NEUTRAL but supportive.
Good luck. I'm betting he will come around if he loves the game as much as you say. He just needs space. Looks as if he's getting pressure now (you just don't realize you are doing it).