Federal Rule of Criminal Procedure 52(b) provides that where a criminal defendant fails to raise an argument in the district court, the appellate court can review the issue for plain error. The Fifth Circuit, as opposed to other circuits, had the practice of refusing to review factual matters not raised before the district court. In Davis v. United States, a criminal defendant was convicted of certain 2016 federal offenses, and the district court held that the sentence should run consecutively with any sentence he would receive from pending 2015 state offenses.
On appeal, Davis argued for the first time that the sentences should run concurrently instead, as he claimed the violations were part of the same course of conduct. The Fifth Circuit, as usual, refused to review for plain error under Rule 52(b). The Court, in a unanimous per curiam decision, reversed and remanded, holding that Rule 52(b) “does not immunize factual errors from plain-error review,” and thus the Fifth Circuit must so review late-raised issues. A link to the opinion is here.