Any umpire, if he notices an illegal movement by the pitcher, can call a balk. The specific rules for balks were first introduced in 1898 to prevent pitchers from intentionally deceiving baserunners. Without balk rules, pitchers had any means of fooling baserunners, who had to act conservatively on the bases as a result.

The History - What is a Balk? A balk is an infraction that can be committed by only a pitcher -- and only when there is at least one runner on base. The rule was created to prevent pitchers from being able to deceive baserunners on opposing teams.

It’s one of baseball’s more intricate rules, with a long list of permutations, sometimes even leading to confusion between those on the field. But the balk essentially keeps the pitcher in check by limiting his ability to fake a pitch or a pick-off throw to one of the bases.

If there are no runners on base, a balk is called an “illegal pitch” and a ball is added to the count This is because he has nothing to lose – if the batter doesn’t get a base hit, then the balk call stands. If he does get a base hit and all runners advance one base, then that batted ball result stands.