The player on the other side -for- cuts in for support.
At the moment the ball is played to the diagonal player makes a breakthrough or lateral move, gets the ball played to him and gets to the shot.
If no goal is scored, the support can shift attention to the other back, where breakthroughs or clearances can be made for the shot.
Note: The player on the side of the ball can also run in instead of the player in front. The action then comes from the other side of the box.Exercise: