We have said that preexisting, factually similar cases are—not always, but (in our experience) usually—needed to demonstrate that officials were fairly warned that their application of force violated the victim's constitutional rights. Officers facing split-second decisions in dangerous or life-threatening situations are seldom provided with fair warning, notice or guidance by a general requirement of “reasonableness.”
See Priester, 208 F.3d at 926 (“In the context of Fourth Amendment excessive force claims, we have noted that generally no bright line exists for identifying when force is excessive; we have therefore concluded that unless a controlling and materially similar case declares the official's conduct unconstitutional, a defendant is
usually entitled to qualified immunity.”)(emphasis added);
Smith, 127 F.3d at 1419 (“A reasonable official's awareness of the existence of an abstract right, such as a right to be free of excessive force, does not equate to knowledge that
his conduct infringes the right. Thus, if case law, in factual terms, has not staked out a bright line, qualified immunity
almost always protects the defendant.”)(second emphasis added)(internal quotation marks omitted);
see generally Marsh, 268 F.3d at 1030–1033 (discussing standard of reasonableness and use of precedents).