weve had conversations here before where people claimed that the wa;ll of three consitutes blocking and theyd ping it. The entire point is to draw defenders right uop to the wall before the pass occurs so maybe that has some validity
It depends on the execution... typically the scrum half passes the ball to one of the players in the wall, and the opposition have a direct line to that player, therefore no obstruction. Of course, obstruction only counts if the ball carrier is unsighted, not a support runner.
The scrum-half will typically run a wrap-around line first... this is the only contentious issue IMHO... there was discussion in my younger years that the furthest player in the wall needed to have possession and offload to the scrumhalf to avoid a blocking penalty (so the wall could be slightly angled and the ball quickly transferred), and I recommend a wall of 2 players to reduce this risk; however, I can't see that being penalised in the modern game that is littered with dummy runners and pull back passes.
If the scrum half does not get the ball back, then the ball is popped to a player running to one side of the "wall", or potentially the wall splits and a runner comes up the middle, but in each of these options there is a clear line between ball carrier and defenders.