Basically, the Court held that once a judge says something that functions as an acquittal, jeopardy attaches. This overcomes any state procedural rule holding otherwise; the state court's interpretation of its rules is not binding on the Supreme Court for purposes of federal constitutional law. The majority opinion, by Justice Scalia, garnered support from Justices Stevens, O'Connor, Souter, and Thomas. That's not exactly the "ordinary" sort of majority in a case expanding the rights of a criminal defendant!