This hand arose in the penultimate round of a four-session, eight-round Swiss pairs event involving the then leading two pairs. EW were playing 2/1 with a short club opening with transfer responses, a 14-16 1NT and a light opening style.
The jurisdiction is Australia with the relevant extract from the ABF Alerting Regulations:
3.3 Alerts during the Auction
3.3.1 If a call is conventional, it must be alerted (unless it requires an announcement or is self-alerting).
3.3.2 Two classes of natural calls must be alerted (unless they are self-alerting), viz.
(a) The call is natural, but there is an agreement by which the call is forcing or non-forcing in a way that the opponents are unlikely to expect. Examples:
(b) The call is natural, but its meaning is affected by other agreements, which the opponents are unlikely to expect. Examples:
Prior to his final pass, North inquired as to the meaning of all bids in the auction at which point it was revealed that West was 15-16 and unbalanced with ♦ support. South called the Director to draw attention to the apparent irregularity of the failure to alert both 1NT and 3♦, but was careful to not suggest what remedy he was seeking (although it was fairly obvious that changing his double to a pass was what he was looking for).
The Director ruled that neither 1NT nor 3♦ were alertable, would not allow South to retract his double and instructed that the auction and play continue. North and East passed, North led ♠A and continued with ♠T which declarer successfully won in dummy with the Q and came to 12 tricks after South pitched a ♥.
The Director was called back to the table with South contending that absent any alerts of West's bids, it was reasonable for him to presume that West was around 11-13 and with East being a passed with a light opening style, he was essentially doubling the auction which he would not have done had he been aware that West could be 15-16 unbalanced.
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