Pure

More specifically...
Go to Single Event Race.
Achievement says "Race or Sprint," but I STRONGLY recommend you RACE. I tried this initially on Sprint and it never unlocked for me.
Make sure AI is set to "Rookie." Set # of laps to 10.
Pick any track (I used Ghost Creek). Use an ATV with an A Class engine, preferably with a Sprint or Race setup.
Start the race, drive normally except that on each jump purposefully hold your trick until you crash. Count your crashes and continue crashing until you get to ELEVEN (very important because the achievement says "more than ten" crashes!). Once you've counted eleven crashes then continue racing as normal through the ten laps. You should be able to catch up with the leader and win the race in this amount of time (the race will take you about 20 minutes total).

This is a VERY easy way to get this achievement:
-Go online with a friend and in the setting for the race, make sure that you turn AI off.

-During the race crash 11 times and make sure the person you are getting the achievement with, let's you win.

-The achievement should unlock after the race is complete.

-This is confirmed to work by kiomx.

I found the following approach even easier, since you got a bit more control about the outcome of the race:

- go to single event race, choose your preferred track (I did it on Ghost Creek), set the number of laps to 8; make sure KI is on easy and use your best ATV (easily done with an A class engine), then start the race

- make sure you come in first place right away (took me a bit more than one lap) and bring some distance between you and the rest of the field
- then start crashing by holding your trick until you touch the ground, crash and keep distance from the field; you should be able to crash at least two or three times per lap without losing first place
- repeat until you crashed at least 11 times
- finish the race, achievement should unlock

Alright so firstly you need to crash 11 times, NOT 10. The achievement can trick you easily.

Secondly this can be done in either a race OR a sprint. Now if you want to be cautious then you should do this in a single event Race with 10 laps and rookie A.I. Simply crash 11 times then just go as fast as you can. You should easily take first before the end.

Otherwise if you want to do this quicker you can get it done in a Sprint like I did. Now you also need to choose rookie A.I and do 10 laps though you want to pick a course that is long enough for you to catch up. I chose Glamis though this was a good and bad choice, I managed to nab first in the last few seconds.

What is good about Glamis is that it has 2 jump chances which makes it easier to get your crashes done without driving off to the side and such. You can crash at the pole that splits the track in half at the start and then crash on each of the 2 jumps and very quickly get your 11 crashes done. After you have 11 you can rush as fast as you can, I recommend getting as much boost as you can by doing an A trick on the first jump and then a A (or B) trick on the second with also a tweaked one. I then boosted right after the 2nd jump on mostly every lap because it was a straight enough distance though also doing it at the start of the lap would work. If you can get this perfect then it works, because it worked for me first try so even if you do a few attempts you should be able to get it done.

The only last thing I can add is that you have an ATV that is A rank and has a lot of acceleration, boost, handling and top speed. You do not need trick at all, you just want an ATV that can do a sprint very fast and efficiently.

There is no need to take 10 rounds as stated in other solutions here, as long as you are a medium or above driver. It takes around 6 minutes.

My setup:

Race - Timber Falls - 3 laps
AI: Rookie
ATV: A with stats 81-100-92-89-14 but it should work with lower ATVs too.

Just drive around normal and do not try to force crashes between jumps for example by leaving the track as that will cost you time. Just drive from jump to jump and crash either by holding the trick button too long or (easier) back flip 180° to land on your head by tapping back twice.

I did 15 crashes just to be absolutely safe and then just raced pretty normal without extensive everywhere-boosting.

In regard to Timber Falls, my route was the following:
- Start the race and hit the first jump.
- Take the higher route on the right over the jump.
- Drive straight forward and pass the red-white sign left. For driving fast in the later rounds, just boost over the small jump without preloading.
- Proceed under the bridge and take the left route, hit the big jump, take the next two curves and then jump straight forward.
- After the landing, take the left route over the little hill.
- After passing the next few jumps you will drive into a little "village"; take the far left route over a bigger jump and through some kind of house.
- Proceed trough the 180° turn and hit THE LEFT SIDE of the big jump with a slight angle to the right. Make sure that your jump leads you to THE RIGHT SIDE ON THE CLIFF which lets you drive underneath a bridge. Thats a major shortcut and will safe you a ton of time.
- From there on, just take the following left turns and you will face the finish.

Following this strategy, i finished my crashes at about 3/4 of round 1 but was still on 10th place. I managed to get first place by the half of round 2. It was done in about 6 minutes.