I think it's just basically common football sense that you should carry the ball with 2 hands.
I noticed too when Glenn intercepted the ball he was doing the Deion thing and holding the ball like it was a loaf of bread. When he came to the tacklers he covered it up but somebody could have come up behind him and knocked it out of his hands easily.
DD is young but the mistakes are becoming glaring and need to be fixed immediately. You just cannot fumble the ball away time after time. I have faith he'll get it fixed.