Force closing allows the app to refresh and may alleviate minor gameplay or loading issues. Our Support team may also request that you force close to download game fixes.
 
To force close the game, double tap on the home button and all your recently used apps will appear. Swipe up the apps you wish to force close. Please be sure to swipe it up completely to confirm that it will be force closed.

If you can't get this to work properly, you can try restarting your device and then running the app. Some players report this resolving the problem outright.