What was once thought to be Duke’s weakness has suddenly become its strength in NCAA Tournament play. In fact, the Blue Devils have been so defensively stifling that none of its four opponents in the South Region were able to crack 60 points against them. So what’s behind Duke’s big turnaround on that end of the floor? Let’s take a look at some key defensive numbers from the last two weeks and compare those with its previous 21 games — beginning with when conference play tipped off on January 3. In its four NCAA Tournament games so far, Duke has reduced its opponents’ scoring by a whopping 15.0 points per game and 16 percent fewer points per possession. Duke’s sudden surge of defensive stinginess is related to two improvements: 1) better success in forcing opponents to miss shots (from both two- and three-point range); and 2) keeping teams from getting to the free throw line. At first glance it would appear that a markedly slower tempo (four fewer possessions per game) might be helping the Blue Devils’ defense, but that assumption could be somewhat deceiving. NCAA Tournament opponents are attempting only one fewer field goal per contest and turnovers and offensive rebounds have remained about the same as they were before. That means that the slowdown is almost entirely caused by the Blue Devils move from rarely fouling to almost never fouling. Opposing teams are averaging fewer than 10 free throw attempts per outing in the NCAA Tournament.