Simple moves and requirements for the individual defender: defensive posture should have knees slightly bent and weight forward on the toes.
How to capture more space and range: Train players to take steps towards the ball before moving. Be able to move laterally and forward and back by keeping a low, neutral position with a slight forward lean.
Drill Idea: Have a group of defenders line up in left back. One at a time hit an attack at the defender and have her dig the ball and then catch the ball. Vary the tempo, height, and depth of the attack. Inspire players to adopt an "I can dig any ball" attitude on the court!