There could be several reasons why your game closed unexpectedly. Here are suggestions that will usually solve issues like crashing or freezing. 
Try rebooting your device.
If you play through Facebook, try uninstalling and reinstalling the game. If you are a Guest user, do NOT UNINSTALL your game.
Try upgrading the operating system on your phone to the latest one. 
Do not run any other applications in the background while playing this game. 
Go to your device settings, into WiFi, and then tap your network to forget it. Then reconnect to your WiFi network.
If these do not help, please send us a message with your support key and as many details as possible.