First, this video helps me a lot to learn how to throw with the spin effect
I tried getting splits with a slow throw. With this method, you get more % of splits, but the splits are difficult to clear (7-10 or 4-7/6-10).
What I did: I throw at the last arrow to the right (I'm not lefty) with the spin effect. This method is less effective to get splits, BUT the splits you get are more easily to clear (I got 2-4-9). And then was just luck to clear that split. Straight throws doesn't work on most of the splits, but luck plays an important role in this achievement. Sometimes when you hit a pin, it "flies" to the other(s), and the split is clear = Achievement Unlock.
Tip: Use a T-shirt. I'm not english native speaker, but fall or winter clothes that cover your arms make more difficult to get the throw like you want.
Good luck with this one :) I played for 4 hours until I unlocked it