Pop up ads is common Thing when you are playing awesome game for Free. But many user accidentally Install some Malware which show them pop up ads without permission or even anytime. And its really easy to remove that suspicious problem. Just follow the steps.
First Try to Know which app causing Problem.
1.Restart your phone or Close every applications
2.Open Settings > Apps > Recently added apps
3.Remember when this pop up ads started and find the suspicious application, which you did not know.
- Force stop it and uninstall it. Clear All Data too.
Boommm. Thats it.now just restart and ads were gone.
(Alternatives)
If you cant found suspicious apps.
- You can do Reset factory settings also. But that willl start your phone as it was purchased.