From Halopedia, the Halo wiki
License to Kill is an achievement in Halo: Reach multiplayer matchmaking added with the Anniversary Map Pack. It was unlocked by splattering 5 people with a vehicle in one matchmade game.[1] The achievement could only be unlocked on an Anniversary map.
Following the shutdown of Xbox 360 Halo online services on January 13, 2022, this achievement is no longer attainable.[2][3]