Baseball is unique in that it condones cheating. In fact you could divide cheating in Baseball into three categories. The first two are okay, but the third one is absolutlig verbotten. Here's the difference in the categories.
The first category of cheating is actually in the rule book. It includes things like stealing bases. Or a pitcher faking throwing to one base then throwing to another. These are permissible. In fact great base stealers like Ty Cobb are the stuff legend. Likewise catchers who throw out runners who attempt to steal are glorified, as in Ivan Rodriguez.
The second category is legal if you can get away with it. This would be things like throwing a spit ball, or scuffing the ball. A hitter might cork a bat. Legendary ball doctor Gaylord Perry is in the hall of fame. The catch however, is that this kind of cheating only takes place on the field. It's a skill that some players develop, like hitting the ball, and we admire them for it.
So what kind of cheating is forbidden in baseball. Off the field cheating. Now what do we mean by that? Well, in the early days baseball some players were paid by gamblers to throw games in the World Series. That is something from off the field that someone brings on the field to change the nature of the game. The more recent version of this is steroids and other drugs. Players who use these drugs change their bodies to make themselves better players or lengthen their careers. But it destroys the integrity of the game. This is why steroids, HGH and the like cause such a big scandal. This why people say that records set by steroid users are not legitimate.