re: Where does the New Orleans Saints' defensive turnaround rank in terms of being unexpected?

I think a good running game and good defense go hand in hand. You run the ball well, keeps your D off the field and gives them more of a rest.
Pass the ball all the time you may have quick scores or quick 3 and outs, INT's etc. Defense is on the field more, tired, giving opponent more opportunities to score.
So it's no coincidence that the Saints D improved once they found this running game.