Battery Draining and overheating when run in the background

When I play a world, then go to the home screen without first leaving the world, the game still runs in the background. If I leave the app running in the background without closing it for too long, my battery is drained quickly, and my phone can easily overheat, even if I'm in another app or turn off the screen. I can also hear game sounds even when the screen is off.

I am using a Galaxy S5 on Android 4.4.2.