An easy way to get this is just to go into quick race, set the track to Canyon 1, set the AI to Exhibition and the game type to Knockout and the start. Then select a craft you are good with and the start the race. Try to get a perfect start, stay ahead of the enemies and every weapon that can be fired backwards should be fired, remember that there are 7 enemies and every lap the one in last place gets eliminated, so try and stay ahead of last place at all costs and when it is the final lap make sure you are in first so you can take the win.
Rinse and repeat 20 times and it should unlock.