Ok ill be honest i got frustrated with this one until i read that RT and LT passes the ball from the ruck to the forwards.
So just get close and just to the left or right of the sticks and get it to one of the props (1 or 3 if you dont know rugby to well) hold hild B to knock the ball over.
If tour strugling but i cant imagine you would be just increase your props kicking ability in the stats editor.