[UmpJM]

dash,

You might want to reword that 1st sentence - it's pretty hard for a pitcher to balk after he's disengaged.

Tim,

In terms of convincing your association, that's a little trickier.

The only explicit documentation I can find specific to the jab step (distinct from the jump turn) is in J/R. I have the "Rule Differences Edition" which, though framed in the context of OBR, notes FED/NCAA differences with footnoted references. On the discussion of the jab step, there is no difference noted for FED (or NCAA). While this is not "official interpretation", it certainly is "authoritative opinion".

[Edited to add...]
Also, IIRC, the Jim Evans balk video which, though again framed in the context of OBR is diligent in pointing out where FED differences exist, explains this as a legal move and makes no mention of anything being different in FED.
[Edit done]

Further, I might suggest that in both the jump turn and the jab step, the pitcher's pivot foot leaves the rubber in a way that is clearly NOT a legal disengage. So, the rules allow the pitcher's pivot foot to leave the rubber in a move treated as "from the rubber". The purpose of the rule is to insure that the pitcher step with his freet foot to the base he is throwing on a pick-off. As long as the move is fluid and continuous, and the free foot gains "direction and distance", it has met the intent of the rule.

I'd probably try something along those lines. Plus, if it's legal in OBR (and NCAA), and there's nothing in FED documentation that says it's not legal, it's probably legal.

John