Baseball, steroids, and jurisprudence

Here is a question for the jurisprudes and the crim law types out there (or just anyone else with an opinion):

In 1991, baseball established by rule that it was against the rules of the game to use a range of drugs, including steroids. There was no testing, no enforcement mechanism, and no determinate punishments for using steroids. That was the state of affairs until the start of the 2006 season, thus it was the state of affairs from 2001-03, when Alex Rodriguez has admitted to using steroids and when he tested positive. Of course, the commissioner did have catch-all "best interests of baseball" powers, so punishment was possible through that power. But absent testing, there arguably was no way ever to find out that someone was using steroids.

So, my question: Has Rodriguez "cheated" or "broken the rules" of baseball (put aside societal laws against steroid distribution, possession, or use) given the legal state as described. Is a stated legal prohibition that is not, as a matter of law, enforceable or punishable, a legal prohibition that can be violated?