Ad blockers for Android pop up all the time, both in and out of the Play Store. Most of the time, since they harm developers and Google, they get smacked down fairly quickly. A few have survived down the years, but in most cases have become severely limited or are forced to partner with ad providers. AdBlock Fast had the special advantage of Samsung's blessing. AdBlock Fast was developed by Rocketship Apps in partnership with Samsung, made specifically to work with Samsung's bundled browser after they opened up their API to third parties, allowing them to do things such as block features of the browser. iOS ad blocker Crystal and the time-tested AdBlock Plus have since incorporated compatibility with Samsung's browser.
AdBlock Fast was apparently ousted from the Play Store for violating section 4.4 of the Developer Distribution Agreement, stating that an app cannot disrupt or interfere with devices, networks or other parties' apps and services. Rocketship developer Brian Kennish received the notice from Google. Talking to our source, The Verge, Google confirmed they removed it, but did not specify why the app actually violated the rule. Since other ad blockers remain on the Play Store, presumably, the reason for the violation was not ad blocking itself, leaving it rather unclear why that was. AdBlock Plus, however, ran into a similar issue and was eventually forced to distribute their app with their own browser, calling the reason for AdBlock Fast's dismissal further into question.
As Samsung had partnered with Rocketship Apps themselves to ensure compatibility between AdBlock Fast and their own browser, Google's removal of the app from the Play Store may cause some tension between them. With Samsung being one of Google's biggest Android partner, it's unclear what, if any, falling out may take place. Neither side has issued an official comment on the matter at this time. Google's own actions to keep mobile web, where they make most of their ad revenue, alive make this issue especially iffy for both sides. It seems that Samsung was deliberately allowing their partners to take actions in a gray area of the Play Store's developer agreement, potentially violating it. There was no word on if and when the app will become available again.