The NYPD is investigating after video surfaced online showing a group of girls fighting inside a Brooklyn McDonald’s while dozens of fellow teens watch and cheer. The video, posted to Facebook, captures the Monday afternoon brawl at a McDonald’s on Flatbush Avenue in Flatbush. The footage shows four girls fighting with another teen wearing a blue hooded sweatshirt while throngs of bystanders shout in the background.The larger group of girls can be seen grabbing the girl in the blue sweatshirts, pulling out her hair extensions and punching her in the upper body. At one point, the girl in the blue...