text: Well, I believe it was put into the code after the Black Sox scandal in 1919. It was used to ban Pete Rose from baseball for life, which was interpreted, by extension, to include the HOF, when he was found to be betting on baseball although no one had any proof that his gambling affected his management of his team. It was said, that in the face of the very explicit language of Rule 21, it didn't matter if if affected his own team or not.\n\nHe couldn't really say he was ignorant of this provision; it is supposedly posted in all teams clubhouses, per Judge Landis, who was the commissioner who inserted in into the rules back in 1920 or so.