Hunting quadrotors with #8 buckshot might be a valid pasttime for some people, but the US Army is looking for a little more refinement.
The device you can see being used to kill an unsuspecting quadrotor is a 'cyber rifle', built by the Army Cyber Institute and demoed at the Association of the United States Army Annual Meeting and Exposition.
The name is a little misleading: it's not really a rifle: it's a Raspberry Pi and a Wi-Fi antenna cobbled together, which takes advantage of a known security flaw with Parrot quadrotors to 'shoot' them down. The rifle shape, according to an interview with Popular Mechanics, is "mostly for kicks".
The familiar shape is meant to make it easier for military brass to understand the tactical application of cyber-weapons: it's not some overly complicated computer; it's just "Aim. Shoot. Crash." The utility isn't limited to drones, either: the ACI also showed it turning off lights and opening the doors of a cute little bunker.