It sure looks like it, even with the relatively lousy batting performance of the union rep. A company contemplating action against a poorly performing employee should always consider whether that employee has engaged in recent "protected activity", such as reporting sexual harassment, or exercising rights under a collective bargaining agreement. Here, the Florida Marlins took action against not one, but two players-- Logan Morrison and Wes Helms, who is a union representative--after Helms told Morrision it was okay to skip a pre-game team function with some season ticket holders after an earlier autograph signing session ran long.
The club promptly (as in less than 12 hours later) demoted Morrison (second on the club in home runs, third in RBIs) to AAA, and released Helms.
While the timing of an adverse employment action is seldom enough to demonstrate conclusively that the employer was retaliating illegally, when the timing is close enough to the protected activity (like here), courts will usually allow the issue to reach a jury. Or an arbitrator.
I suspect that the club was trying to send a message, and is willing to deal with the negative consequences in any arbitration down the road. This is simply too heavy handed to be anything but a deliberate bean ball by the Marlins management.