I'm working on a complaint to US federal agencies. One of the arguments I need to make is, a company cannot use existing laws or policies or instruments as both a sword and a shield. That is, they cannot apply an instrument as a defensible position in one circumstance, and then use the same instrument for offense in another circumstance.
I know US law does not favor dual uses like that. For example, in the Anthem Data Breach settlement, Anthem tried to use security evaluation reports for defense by saying, "security firms that performed the evaluations said everything was OK" [sic]. Then, Anthem tried to say the reports were not discoverable because it was protected work production. Judge Koh disagreed and ordered the Anthem to turn over the reports stating Anthem could not use them as a sword and a shield.
My question is, is sword and shield a doctrine in US law? If not, then what is it called?
(I'm getting lots of hits explaining the concept, but I'm not finding the legal underpinnings).