can a goalie pick up a back pass
Goalkeepers are allowed to handle the ball if the ball is played back to them by an action other than a kick or throw-in (such as a header), but defenders are not permitted to attempt to use a deliberate trick to pass the ball to the goalkeeper with a part of the body other than the foot to circumvent the rule. This would include flicking the ball up with the foot and then heading the ball back to the goalkeeper, or heading a ball on the ground that would otherwise be regularly playable with the foot.
Back-pass rule