As unbeatable as the top four are, it seems that there is certain kinds of players each one of them has been known to have issues with. Nadal and Murray can sometimes be blasted off the court by ball-bashers having a a great day. Fed can sometimes fall into a UE-fest when faced with a well-defending player that puts consistant pressure on him with groundstrokes. Djokovic however doesn't seem to have any pattern like this, at least as far as I have seen. He's great at neutralizing the ball-bashers as well as grinding it out with the great defenders. Is there any certain type of player that Djokovic has been known to struggle with over his career?