Zebra put thumb-size battery-powered beacons in every player’s shoulder pads that emit 12 pings a second. Receivers installed in about half the stadiums in the league picked up the signals. The data was sent to servers in the press box, where each player’s X, Y and Z coordinates were mapped on a computer and shared with broadcasters. Zebra employees also cataloged every play.
Source: In a Data-Driven N.F.L., the Pings May Soon Outstrip the X’s and O’s – The New York Times