Law Discussion: Try or No Try?

The Stormers play the Crusaders at Newlands. Gio Aplon puts a foot into touch and Kieran Read takes a quick throw-in which Dewaldt Duvenage intercepts and races away for a try. The referee awards the try. He then sees the assistant referee with his flag in the air and goes off to consult him. The assistant says (twice) to the referee: "Foot in the field of play. Advantage applies." The referee cancels the try and awards a line-out to the Crusaders.

Law 6.B.5 (d) When to lower the flag. When the ball is thrown in, the touch judge or assistant referee must lower the flag, with the following exceptions:
Exception 1: When the player throwing in puts any part of either foot in the field of play, the touch judge or assistant referee keeps the flag up.

The assistant referee did the right thing in keeping his flag up. It is what his job description requires. But he also said: "Advantage applies."

Does advantage apply?

Law 8 Advantage
DEFINITIONS
The Law of advantage takes precedence over most other Laws and its purpose is to make play more continuous with fewer stoppages for infringements. Players are encouraged to play to the whistle despite infringements by their opponents.

That implies that advantage happens when there is an infringement.

Is putting the foot into the field of play an infringement?

Law 19.6 HOW THE THROW-IN IS TAKEN
The player taking the throw-in must stand at the correct place. The player must not step into the field of play when the ball is thrown. The ball must be thrown straight, so that it travels at least 5 metres along the line of touch before it first touches the ground or touches or is touched by a player.

Stepping into the field of play is wrong.  The throw-in is incorrect.

19.7 INCORRECT THROW-IN
(a) If the throw-in at a line-out is incorrect, the opposing team has the choice of throwing in at a line-out or a scrum on the 15-metre line. If they choose the throw-in to the line-out and it is again incorrect, a scrum is formed. The team that took the first throw-in throws in the ball.

There is a sanction for an incorrect throw-in. It is the same sanction as there is for a crooked throw-in, i.e. the option of a scrum or a line-out.

Could advantage then be played?

Law 8.3 WHEN THE ADVANTAGE LAW IS NOT APPLIED
(a) Referee contact. Advantage must not be applied when the ball, or a player carrying it, touches the referee.
(b) Ball out of tunnel. Advantage must not be applied when the ball comes out of either end of the tunnel at a scrum without having been played.
(c) Wheeled scrum. Advantage must not be applied when the scrum is wheeled through more than 90 degrees (so that the middle line has passed beyond a position parallel to the touchline).
(d) Collapsed scrum. Advantage must not be applied when a scrum collapses. The referee must blow the whistle immediately.
(e) Player lifted in the air. Advantage must not be applied when a player in a scrum is lifted in the air or forced upwards out of the scrum. The referee must blow the whistle immediately.
(f) After the ball has been made dead. Advantage cannot be played after the ball has been made dead.

None of these applies to a foot-fault at the line-out. Therefore advantage should apply, just as it does for a crooked throw-in.

Giving the line-out throw to the Crusaders was palpably wrong.

Certainly it makes no sense that a team should benefit from its own mistake, as was the case here.