But the Supreme Court and other appellate courts have failed to follow any consistent practice about sua sponte holdings. The difficulty courts have is illustrated by the fact that even the most prominent appellate judges sometimes say they want procedural regularity, but in other cases exercise the freedom to do what they like.
Barry A. Miller,
Sua Sponte Appellate Rulings: When Courts Deprive Litigants of an Opportunity to Be Heard,
San Diego L. Rev.
Available at: https://digital.sandiego.edu/sdlr/vol39/iss4/4