The most common solutions for the game force-closing or crashing are:

1. Reboot your device

Often crashing problems are caused by conflicts with other applications running in the background.  Usually these problems can be resolved by fully powering down your device and rebooting.  

Please note that you need to FULLY power down your device by holding down the power button until the device asks you if you'd like to shut down, and then selecting "Shut Down".

2. Cool it down

If your device suddenly shuts down in the middle of a game and restarts itself, this may be an overheating problem. (You should notice that the device feels warm).

To avoid overheating, please make sure that you don't have other apps running in the background while playing.  Also make sure you are using your device in a well-ventilated area (eg., not resting on a couch cushion), that you are not using it in direct sunlight, and that the brightness on your screen is turned down.

3. Uninstall and reinstall the game

Uninstall the game, and then reinstall the game through the App Store.

Please note this will erase any save game data, high scores, and unlocks you may have.