What is the test for reasonableness in determining whether a police officer has been found to have used excessive force against a civilian plaintiff?

"For a constitutional right to be clearly established, its contours must be sufficiently clear that a reasonable officer would understand that what he is doing violates that right." Hope v. Pelzer, 536 U.S. 730, 739, (2002). While the reasonableness inquiry may not be undertaken as a broad, general proposition, neither is official action entitled to protection "unless the very action in question has previously been held unlawful." Hope, 536 U. S. at 739.