NFHS legal windup

[SMEngmann]

Thank you everyone for providing the rule references, I'm glad I now know the exact rule so I can teach my players accordingly, and I will do so. The part that I don't get is why this rule exists in the first place? As an official, I understand that the umpire had to call it according to the rules, but this rule does not make any sense. The intent of illegal pitch/balk rules is to prevent deception and quick pitching. This rule, frankly, does not do either and it is evident in the differences in rule between Fed, NCAA and MLB. Can anyone explain the purpose of this rule or defend why it shouldn't be changed?