The line comes from Halo 2, released in 2004 by Bungie, where voice actor Jeff Steitzer recorded the multiplayer announcer calls for medals and events. Killing Spree marked five kills in a row, part of a ladder that continued to higher streak medals in later games. As Halo clips moved to YouTube and streaming platforms, the callout became shorthand outside the series too, used alongside other FPS announcements like Enemy Spotted and bomb has been planted to mark momentum in shooters.