Bomb Carrier Kill
From Halopedia, the Halo wiki
The Bomb Carrier Kill Medal is awarded for killing an opponent who is carrying a bomb. It is available in all Multiplayer Assault gametypes, and has a Bungie difficulty rating of a 3 out of 10. It is represented by an octagon with a targeted bomb. As you get this medal, the announcer will say "You stopped (player)." It is one of the more simple medals to get as you only need one kill on the bomb carrier.