In order to unlock this achievement you need to win a game of 9 ball. In order to win a game of 9 ball, you have to pot ball 1 through 9 in order. Once all of the balls are potted, you can then sink the 9 ball. Please note, if you sink the 9 ball off the break, it is an automatic win, netting you another achievement for sinking the 9 ball with the 1 ball still on the table. Additionally, you can use any ball, as long as it is the next one that needs to be potted, to sink the 9 ball using a plant shot. For example, you have already sunk balls 1-4 and are on 5. If you have a clear shot to shoot the 5 ball into the 9 ball, subsequently potting the 9 ball, that is a win. This achievement can be done in career, or multiplayer. The following video shows the 9 ball being potted off the break.
Video credit goes to Pleads.
I hope this solution helped! Leave a comment letting me know if there is any room for improvement! Thanks.