Hi Seren,

I would start by teaching them the correct body positioning, as attached below. Ensure they maintain an open body position, which will allow them to see the player and the ball. Once they have understood and mastered this, you can get the static plater to begin to move along a straight line - this will allow your defenders to keep this positioning on the move. You can then build this up to add a ball in - this will ensure your defender is not simply looking at the player but they are aware where the ball is and can go for the interception. For example, see 1 vs 2 Guarding Ball Side.  

Other drills to help your players master stage 1 defence - shadowing and going for the interception is Defenders Dictating Play . 

Once your players have understood their correct body positioning, you can begin to work on going for an interception. Ensure your players take the ball away from the player and run their feet onto the ball to avoid contact. Your players can then practice it in this team drill. 

If the attacker does get the ball, it is important the defender recovers quickly to do second stage defence, the 3ft mark. Your players can then practice in this group drill. 

The final stage of defence is stepping up and closing the attacker down. You can build this up by simply getting the attacker to pass the ball off to a spare post and then the attacker will try to get down court, the defence would need to step up and dictate where the attacker goes. A harder drill to practice this is