When the police/military/other supporting group to the scene only after the hero has defeated the monster, killer, or Big Bad. Sometimes this is played for humor, or to play up their uselessness compared to The Hero. Often, though, it serves the same purpose as No Ontological Inertia -- while the hero has to defeat the Big Bad alone for the purposes of the story, The Cavalry is necessary to sweep up loose ends and ensure a happy ending, especially in real-world settings where the hero is on the side of law and order. Thus, they'll arrive just too late to interfere in the big fight, but just in time to handcuff the crooks... and to ensure that the hero isn't anticlimactically killed by a stray remaining mook or some other logical but narratively unimportant danger that wouldn't necessarily