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I'm looking for something different from Word for “to use someone's own tactics against them”. I'm considering a scenario in which one intends to use a certain tactic to defend oneself against some enemy. However, before the tactic can be used, it is stolen by the enemy and used against the person him/herself.
Example: Alex told the plagiarizer he'd sue them unless they delete the video. However, that only prompted the plagiarizer to ______ with a defamation lawsuit.