Without explanation, the U.S. Court of Appeals for the Third Circuit has quietly reassigned the judge overseeing high-profile antitrust litigation in Pittsburgh. The move is rare, but the silence around it is rarer, still, according to Pennsylvania legal observers.

When a court of appeals reassigns a district judge, its reasoning for the change becomes part of the body of law that guides judges in their conduct and the absence of an explanation could set a troubling precedent, some said.