So, as far as we can tell it, a pitcher can't have the following substances with him on the mound:

Pine tar
Emory board
Saliva
Vasoline
Mayonnaise
Human excrement
The severed fingers of small children

And now, you can add ... cabbage. A Korean baseball league has told one of its best pitchers that he can no longer wear cabbage in his hat to keep cool during games. The league says, "In common sense, it is difficult to consider that wearing a cabbage leaf will affect pitches. But since it has become a controversy, we decided to set a limit on the boundaries of foreign substances."

We somehow imagine Kim-Jong Il having something to do with this.

Korean League Bans Baseball Cabbage Pitch [BBC News] (via SportsHooligan)