Rookies struggle to pick up NBA defensive schemes because they are so much more sophisticated than at youth levels. When players are younger, they are taught the more elementary task of staying with their man without worrying about funneling him into help. As they get older, their responsibilities increase, but nothing compares to the NBA.
This is where we need to point out an error Zach LaVine makes out of inexperience. Most defensive schemes ask guards to force their man to the sideline when they are running a wing pick and roll because it shuts off all the options available from the middle of the floor. The only schemes that don't force the ball-handler to the sideline are ones where the big man is coming to trap, which clearly isn't happening here.
But instead of forcing John Wall to the sideline, LaVine squares him up as if he's only worried about a one-on-one battle. All Wall needs to do is brush off Marcin Gortat's screen and he has the easiest jumper he'll take all year. There's a lesson LaVine will surely take to heart.