I was hoping they'd explain just why the phrase is so aptly applied, but they didn't. So here's an old post of my own:
The phrase "O. K. Corral" has been invoked on the floor of Congress numerous times as an argument in favor of gun control measures that would limit firearms to policemen and officers of the law. If such measures are meant to avoid the O.K. Corral, how to interpret the fact that it was precisely such a law that precipitated it? It was the attempt to enforce Tombstone's gun control law that was the proximate cause of the gunfight. A even worse problem is that the survivors of the losing side got themselves deputized by the Sheriff and went after the town and Federal marshals. A police-officer-only model of gun control would have done nothing to avoid the shootout, or reduce the violence that followed it.
The one thing that did reduce the violence is the very thing that Congress most hates to consider: citizen vigilantes, who informed the participants that any future shootouts had better be conducted outside of town or there would be some hangings. This maneuver was so effective that historians still have trouble deciding exactly what happened in the rest of the war between those factions, as very little of it occurred close enough for nonpartisan witnesses to view.