Please try the following steps which have helped lots of players to solve the crashing issues.
 
1) Check whether your device meets the minimum hardware requirement. Menu > Help > Hot Topics > What are the device minimum specification. For example, 1GB RAM.
2) Check that your device has enough free storage space. Lacking of space can result in crashes, slowness and other unexpected issues in any app. Please go to Settings > About and check Capacity and Available. You can free up space by removing unnecessary apps, for instance.
3) Free up device memory by closing apps that are running in the background.
4) Turn your device off and then on again, and launch the game. The device memory should be free at this point and the game performance should be improved.
5) Uninstall and reinstall the game. This step can fix most of the mysterious issues.
6) If you are using a jail-broken device, there's no guarantee that our game will run without issues, or that the issue can be resolved by any other way than by resetting your device entirely.
7) If you are using an emulator, it's expected that the game won't install or won't load.