Stay compact

 This for the defensive shape. Basically the whole team stays compact until the force the ball to the line on either side. By line I mean to the winger or to the fullback. that's when we initiate our press and shift towards one side. 

We have a system where the pitch is split vertically into 5 zones the defense stays within the middle three zones staying compact. once the ball goes to zone 1 or 5 which are the ones on the both wings. The team presses and closes them down and steals the ball. once the defense shifts there should be 2 zones on the opposite flank unoccupied.

Another reason for fullbacks to stay compact until the ball is played out is. Because if they move towards the line early the opponent may play the ball in between the fullback and the CB on the fullbacks side, therefore splitting the defense. 

That's it