Benefits
- Develop Ground ball technique in a more realisitc situation
- Defense learns to communicate
- Learn how to adapt to unsettled situations
- Increase ability to clear under pressure
- Offense learns to find the open guy

(left image)
5 offensive players and 4 defensive players in front of the goal.  It is important to not let them start in any type of formation as the goal is to let them sort things out in chaos.Coach stands up top ready to throw the ball to create a ground ball
The goal of the offense is to score.  The goal of the defense is to run the ball over the midfield line or throw the ball back to the coach.

(center image)
The drill starts when the coach rolls the ball out to open space.
Players must then decide
:
Do I go for the ball?
Do I get open for the pass?
Do I take man?
Do I sluff in?
Much like when a ground ball happens in a real game

(right image)
Once the offense scores or the defense clears the coach immediately sends out another ball before everybody has a chance to settle back in.
In this picture the defense more then likely just cleared, thus the coach is now throwing to open space on the opposite side forcing everybody to re-adjust.
Ideally you would want to do this at least 3 times before the next group 5 offensive players and 4 defensive