The Duke player was going for the block when all of a sudden there was no ball to block. The Duke player tried to pull his arm back and when he did his elbow made contact with the North Carolina player's face. Because of the momentum of flying in the air, the Duke player had his back to the North Carolina player when the contact was made. When you're airborne you have no idea where you're going to come down and it just so happened that his elbow came down on the North Carolina player's face.