The First Amendment does not apply to private organizations. Even so, I support the pitchers. Pitchers not perverts!
There is such thing as religious protection in the workplace. Yes you trade your freedom for money. But not totally.
These men have a good case that their employer cannot require they were symbols supporting a sinful worldview when it is not directly required for them to do what they were hired to do (pitch). I believe they’d win in court.
Now if you are hired as a bartender and then say you can’t serve alcohol cause you are a Mormon that’s different. One cannot reasonably be a bartender and not serve alcohol.
But you can play any position in baseball without wearing a conscience offending emblem on your uniform. Your employer cannot require that you do so, legally.