IPhone white screen when I opened app?

So i clicked on one of my apps, and it went white. Not the whole screen, you can still see the time and battery percentage, etc. But it won't let me go to the home screen, nor turn it off or anything. Any suggestions? Should I just let the battery die?

It won't let you close the app! It won't turn off!
Well if it won't turn off or exit the app, wait for the battery to die and DELETE THE APP when it turns on!