Bone Cracker
From Halopedia, the Halo wiki
Summary
The Bone Cracker Medal is awarded for hitting and killing an opponent with a melee attack. It is available in all Multiplayer gametypes and has a Bungie difficulty rating of 3 (out of 10). It is represented by an inverted star with a fist. After you kill an opponent with a melee attack, a message appears on your screen that says: "You beat down (player)".