RR led his singleton spade, which was not everyone's choice as the bridgemates showed, and dummy went down. "Can you put the trumps on the left, please?" RR asked politely. "There aren't any trumps", SB South replied. "East, ChCh won with the ace of spades and SB as South dropped the king."
ChCh paused for thought and looked at the NS convention card before switching to the queen of hearts. SB misguessed to play low and ChCh continued with another heart. RR cashed the ace of hearts on which all followed, but he was unsure if his remaining heart was a winner. After an age he decided to chance it and cashed the nine of hearts for one down.
SB was furious. "Directooooooooooooooooooor", he bellowed. OO arrived. SB began his rant: "East took advantage of RR's clear mistaken belief that it was a trump contract - probably 4H, the contract on the previous board. This arose from RR's request to put the trumps on the left". He continued: "When East won the first trick with the ace of spades and I dropped the king, it was normal for East to continue spades, but he switched."
"Law 73C1 states: When a player has available to him unauthorized information from his partner, such as from a remark, question, explanation, gesture, mannerism, undue emphasis, inflection, haste or hesitation, an unexpected alert or failure to alert, he must carefully avoid taking any advantage from that unauthorized information [see Law 16B1(a)]." He pauwed for breath. "The slimeball ChCh did not do that. Indeed he worked out the lead was probably a singleton".
ChCh was quick to respond. "That remark is a breach of Best Behaviour at Bridge", he began. "And I did consider that partner might have led from Qxxx in spades, but the NS convention card did not have "possible singleton" ticked for 1NT, so I ruled that out. Also, RR would not have led the 3 from Q632. If he had Q63, SB would not have dropped the king from K2"
How do you rule?