Halo: Reach

To get this achievement you must get a kill in a match-made rocket race.

First of all, to get rocket race, you must participate in the 'Multi-Team' playlist.

To get a kill in a Rocket Race match, you must kill someone when they are off their Mongoose, as you are invincible when you are riding around. You preferably want to be the passenger getting driven around so you can just concentrate on shooting, otherwise you'd have to get off just to shoot. There are always people in RR who don't know what they're doing so it should be easy. Look for Red arrows who seem to highlight people who are not on their Mongoose for some reason and just launch rockets towards them when you have a clear line of sight.

As mentioned below, you can also splatter them with your Mongoose!

To earn this achievement, you simply have to kill an opponent in a rocket race game. The Rocket Race game is ONLY found in the "Multi Team" playlist, and this playlist has 12 players in it. Because of the large number of players, it is unlikely that you'll actually play Rocket Race so I recommend getting the largest party you can get (guests are fine) and head into Multi Team. If you get rocket race and you have a friend on the other team, meet up somewhere on the map and kill eachother. You cannot die when you're on the mongoose so the player dying has to get off.

If you do not have any friends in the game, simply drive around looking for red arrows. These indicate players who are not on their mongoose, and therefore are able to be killed.

*Edit - "nel e nel" has this bit of advice for people:
If you don't have friends to boost with, you can use the rocket splash damage to knock people off the Mongoose. Don't hit the Mongoose directly as it will have little to no effect, you want to aim next to it or in front of their path. This will cause them to go flying and tumbling, and if they land upside down they will automatically get thrown off in order to flip over their Mongoose. When they are scrambling - BLAM - hit them with another rocket. Should be pretty easy I got two double kills in under 5 minutes in my first time ever playing Rocket Race.

Goodluck!

You can get this achievement in the ROCKET HOG gametype using the hog's rocket launchers. Arguably this is the easiest way to get this achievement without boosting. Fire your rockets at an enemy hog, flip it and the last few rockets from your volley will not only net you your achievement but a double or triple kill medal if you're lucky.

I got this achievement within 30 seconds of starting the Rocket Hog mode and netted a perfection medal shortly afterwards as well.

Rocket Hog is a Multi-objective game type.

This achievement is a lot easier to get now due to halo reach being backwards compatible. There have been up to 25,000 players online after this update for the Xbox one which changed significantly as reach was only getting around 5,000-6,000 players when it wasn't backwards compatible.

To get the achievement go to matchmaking and select the "EVOLVED" category then select the "MULTI TEAM" playlist.

Search for a game and make sure you vote for a map that reads TU Hog Race (Which is rocket race) If you don't get this in the first 3 maps (generally this happens) then select none of the above and hog race has more of a chance to be in the next 3 maps you can vote for.

To get the actual achievement you must kill someone in rocket race. The only way to damage someone in rocket race is to shoot them when they are out of their warthog or you can splatter them, however you must be the driver if you want to splatter them for the achievement.

Make sure you flip their warthog to get them out or just generally shoot them when they are out of it and if you are the driver then try to splatter them or jump out. If you do jump out you are vulnerable and you can have just as much a chance of being killed as they are!

If you die or your warthog gets flipped then you will spawn/you can get inside another part of the warthog meaning you won't be locked in one seat throughout the whole game which allows you to use the rockets, passenger or drive

You should be able to kill the person you are trying to kill when they are out of the warthog and the achievement will pop up straight after for 20G

Hope this helps!

This is a VERY easy achievement!!

Go into a Multi-Team game then do a Rocket Race.
Simply just wait until a person gets out of their vehicle and splatter/shoot them. Look for red arrows to highlight people that you can attack. Some people in RR don't know what the hell they are doing, so I would go for them. I hope this helps!! :D

Voila!