Police officer Daniel Rivas-Villegas responded to a report that a woman and her children were barricaded in a room because Ramon Cortesluna threatened them. During the arrest, officers saw a knife in Cortesluna’s pocket, and Rivas-Villegas briefly placed his knee on Cortesluna’s back while the knife was removed. Cortesluna sued under Section 1983, alleging excessive force. The Supreme Court held that Rivas-Villegas was entitled to qualified immunity because no precedent clearly established that this particular use of force was unlawful. The Court distinguished the cases on which Cortesluna relied, emphasizing differences in the duration, location, and circumstances of the force. It reversed the Ninth Circuit’s determination that the officer was not entitled to qualified immunity.