A is huddled with 11 players. A12 runs off the bench and his teammates in the huddle see him coming and wave him back. He does a 180 and returns to the bench. He does not communicate with anyone in the huddle. Ruling?

I got nothing. A substitute becomes a player when he enters the field and communicates with a teammate or an official, enters the huddle, is positioned in a formation or participates in the play.

Sounds like he never got a chance to do any of this. Besides, you really don't want to make this kind of call.

No foul,
The substitute never became a player (2-30-15), And (3-3-1) states that no substitute shall become a player and then withdraw and no player shall withdraw and re-enter as a substitute