This one is actually the hardest achievement in this game due to the fact that you can run by double tapping an arrow key.
First of all, skip the tutorial using the down arrow key.
Build the camp, hire archers and a builder, build wooden barricades on both sides of the camp.
Your main purpose (aside from not running) should be to survive until Day 10. I think having wooden walls and 5-6 archers should be enough, but you can get more archers, if you prefer. Just don't stray too far from the camp.
Why Day 10, you might wonder, if the title mentions the Ninth Day? Actually, I was able to unlock this achievement by not running until Day 10 and then running on that day. Judging from some other people's comments on the Internet, it seems that the description is wrong, and you need to wait until Day 10 to run.
Also, even if it seems that you didn't run even once, sometimes this achievement still won't unlock.
A couple of tips that helped me get this achievement:
1) Always wait at least 3-4 seconds after stopping before moving again.
2) Don't move while your horse is eating the grass. Wait until it raises its head.
Hopefully these tips help you get this achievement. It can take you several tries, but don't get discouraged: it can be done.