Balks and hit by batted ball...

[Rbn3]

I certainly agree that the phrase "drop his hands..." comes in the context of the quick pitch rule. But elsewhere the rules are more explicit. For example, it could say "except if the pitcher throws the ball to a base." The simple declarative sentence using the word "must" seems unambiguous that dropping the hands to sides is mandatory when disengaging the rubber.

Using the rule you quoted, I cannot imagine the first few inches of movement to throw to first while straddling the rubber could be discerned to be different from the first few inches of starting a pitch, like breaking the hands and lifting the front foot. This makes such a move a balk by the rule you quoted.

I constantly coach our runners that until the pitcher comes to his "stop" in the set position the only place he can legally throw is to a base. Thus, think only "back" until the stop. Obviously, a step off with the pivot foot should also trigger the "back" response.

The intent of the balk rule seems to be to prohibit deceiving the runner, not the batter. The "step ahead of the throw" rule is negated when the pitcher is an infielder (i.e., when he is not on the rubber). It seems to me that when in one continuous motion the pitcher steps back and slings to first, his intent is to deceive the runner. The plain language of the rules requires the dropping of the hands when disengaging.

If you tell me the tradition and common law is that this rule is not interpreted as a "must" in all circumstances, so be it.