From Halopedia, the Halo wiki
The Killing Frenzy medal (known as Running Riot in Halo: Combat Evolved and Halo 2) is a multiplayer and Spartan Ops medal awarded for killing 10 opponents in a row without dying. In campaign and Firefight it is awarded for killing 20 enemies in a row without dying. In Halo: Spartan Assault and Halo: Spartan Strike the medal is awarded for killing six enemies in a row without being hit.
The medal is represented by a bronze 5-sided star with a green target in the middle. In Spartan Assault and Spartan Strike it is represented by a stylized shield. When a player earns this medal, Jeff Steitzer will shout “Killing Frenzy!”.