In a recent 3rd grade (8v8) game the coach played her two defenders one behind the other.  Although they were a good team, they gave up too many goals.  The attacker only had to beat one defender at a time.  This is much easier than beating two defenders.

Her players had a problem in that the right defender wouldn't leave her side of the field to help the left, and the left wouldn't leave her side of the field.  The solution is to convince them they don't have side responsibility at this time, but BALL and COVER responsibilities.

 

One defender (the closest) must call BALL and pressure the defender.  The other must move into a supporting position and call COVER! so the other defender can become more aggressive and maybe take the ball away.

 

If the 1st defender gets beat, the 2nd defender steps up and pressures the attacker, while the other defender drops back towards the goal into a position where she can now COVER the other defender.

The classic mistake of players when beat by the attacker is to chase the attacker.  When beat, players drop towards the goal to provide cover or to defend other attackers.