I was observing a game the other day and saw a miscommunication that resulted in a player essentially cheating. This was at an FNM.
- Andrew confirms his move to attacks and declares thopter token and Infiltrator as attackers. They resolve the Infiltrator's trigger
- Nick says "before blockers, Subtle Strike" placing the card on the table near Andrew's thopter and waiting for Andrew.
- Andrew then says, "in response, cast Built to Smash" placing the card from his hand directly on the thopter.
- Nick then replies, "then I'll give your infiltrator -1/-1 and put a counter on one of my Daredevils".
What ended up happening was Andrew just let this happen since he recognized that Nick had not finished casting the spell when he announced his Built to Smash. Technically speaking Andrew is the one who made an error in this manner, but it was clear to everyone watching that Nick intended to give the thopter -1/-1 and manipulated the communication to his benefit.
What should be done if behavior like this is observed? If the answer as a player is to report to a judge, then what would a judge's course of action be?