Stuck with unwanted advertisements in-game
You can force the app to close and then reopen it:

 1. Double-click the Home button.
 2. Swipe left or right until you have located the app you wish to close.
 3. Swipe the app's preview up to close it.


Now reopen the app from the Home screen and you should be set.

Pro Tip: Sometimes tapping excessively with an app can cause it to slow down, freeze or lock up like you describe.