When I first heard a Ninth Circuit judge had requested sua sponte for the parties in Washington v. Trump to submit briefs on whether an en banc panel should rehear the TRO challenge I thought there must be some mistake.

https://twitter.com/mattdpearce/status/830197611273392128

Sua sponte means on the initiative of the court, or on its own motion. A sua sponte action is very unusual as the tenets of our adversarial system normally rely upon the parties to bring desired motions to the court and not the other way around.