In Supergirl: Crisis on Earth X, Kara gets into a fight with
her villainous counterpart.
During this fight, she gains the advantage by bashing her fists together, creating a shockwave that stunned
The camera seemed to focus on this action, and it seemed significant insofar as it let Supergirl gain the advantage in what was otherwise an even fight. It definitively seemed like a continuity reference: “Look, this is what Kara has that makes her stronger.”
However, I’ve watched all the episodes of Supergirl, and don’t recall her ever using this technique. Was it a callback or reference to something? Something that occurred in another show, or in the comics? Or a reference to something that someone other than Supergirl did?