App stuck while downloading at stage of 2%
Tap the Ninjump app icon once so as to pause the download. Turn on Airplane Mode in the settings. Immediately hard reset the iPhone (Sleep/Wake (Power) + Home button held simultaneously until the Apple logo is seen). Once the iPhone restarts, disable Airplane mode, allow it to connect to Wi-Fi. Usually this will have removed the app by now.

If unsuccessful, the next step will be to sign out of your Apple ID in Settings or the bottom of 'Featured' in the App Store, and repeat the process above.

Failing those two, the process can be repeated while incorporating signing into a different Apple ID to get it unstuck...and lastly a restore in rare cases.