Baseball is an outdoor sport and there is a huge fan following in America. Professional baseball players are part of this sport that has professional setup. It has a coach, manager
and many other important staff members that work with the team and players. Professional setup demands professionalism from the players involved. It includes ethics, rules and regulations that are part of the job. When players sign up they become a part of this setup. They are bound by the contract with their employer. Even though it is not same as office job in any way it is still somewhat similar. It is still a professional job that demands high standards. When money is involved in any sport and stakes are high, there is no room for mistakes from players. Players can play the sport hard on the field. Everything that happens on the ground, stays on the ground.
Team reprimanded the player who tweeted disparaging comments on twitter about an opponent is totally justified. It was done outside the playing area and in the public domain like twitter. Twitter is not a battlefield or sparing arena. Players have the responsibility to respect their opponents off the field and in general public. They should be aware that rules of the country take precedence in public. They have to abide by the laws and should not violate 1st Amendment of anyone. When they do, they can get fired. 1st Amendment cannot save them from getting fired from job if they violate any clause in legal agreement.