Ten years ago, the media in Louisville, Ky., could have gotten away with reporting this weekend’s events this way: A group of 10 “roving teens got into a fight with two girls … then it happened a few more times over two hours.” But now, less than 24 hours after a mob of 30 black people roamed through the city’s downtown Saturday, beating, laughing, destroying property, sending three seriously hurt people to the hospital and walking away laughing, outraged citizens in Louisville are asking two questions: Why is black mob violence such a problem? And when is local media going...