This achievement is for acquiring a special trick in a race event in less than 30 seconds. I got it in just under 29 seconds.
Load up the map Ghost Creek under the Single Event part on the menu screen, but make sure you have an ATV with high acceleration and tricks. An A class engine would be helpful.
Keep doing tricks including the LB/RB combinations for them starting off with A, B and then Y, and you’ll soon get it - this was my attempt in the video above, bear in mind this took me about 50 attempts as my coordination isn’t that great!
Good luck!