That being the primary duty of the role. Effectively, Bonnucci doesn't offer much other than being able to hold the ball and send it long. Thats actually one reason why he kind of complements Chiellini and Barzagli who have every other facet to their game, except perhaps being clumsy on the ball. For me, Bonnucci lacks the awareness and positioning you'd associate with a quality defender. And while they both (Martin and Leo) tend to be error prone, I think Caceres reads the game a bit better, and most importantly always plays within himself.