... well, in the real world, over here in the US, there are these entities called corporations When a person accepts a position with a corporation, that person agrees to abide by the rules of that corporation, more specifically, corporate policies and code of ethics, and while neither can go against the US Constitution, they still can contain certain policies and guidelines which, if broken, are valid grounds for dismissal or punitive action. One that always pops up in every corporation's code of ethics is the "image" of the corporation (this is why you hear of employers asking employee candidates for their Facebook passwords).

The NFL is a corporation. The "commissioner" is really the CEO of NFL Inc., appointed by the Board of Trustees (owners)
It would be rather easy to argue in court that Williams, Payton, Loomis and Vitt, as employees of NFL Inc., had tarnished its image by their actions.