to get free in the circle requires the shooters to actually play a defensive role first and attack second.  this is normally done by defending from behind or to the side as most defence players will defend from the front, and most wont realise they are the ones being defended til too late.  if your shooter positions themselves close to the circles edge, keeping their body in between the goal ring and the defence player and therefore keeping the circle wide open for the shooter to drive into the space either using a lob pass, or a pass from the other side of the circle leaving the defence wondering what happened.  most defence players are a lot slower at getting away from players as their main skill is defending not attacking.