Implicit Length Showing

Dealer:  South Vul: N-S	Betty ♠Q ♥KQT63 ♦J832 ♣JT9
William ♠A4 ♥J9752 ♦T ♣A8762		Michael ♠JT852 ♥84 ♦75 ♣KQ54
	User123 ♠K9763 ♥A ♦AKQ964 ♣3

South	West	North	East
User123	William	Betty	Michael
1♦	2NT	Pass	3♣
3♠	All Pass

Opening Lead: ♣ A

Playing on BBO, William and I were playing against a partnership that didn’t know each other. We set their 3♠ contract, but why were they playing spades instead of diamonds?

First, some background for those of you not familiar with BBO. It’s a great place to play bridge online, either with people you know, or with random people. However, if you are playing with a random partner, it is easy to end up on a different page from your partner as to what bids mean.

Put yourself in Betty's shoes. You hold:

♠Q  ♥KQT63  ♦J832  ♣JT9

What do you think your partner has after the bidding has started as follows?

1♦  (2NT)  P  (3♣)
3♠   (P)   ?

The only thing you know about your partner's 1♦ is that it could be short, but otherwise, your partner is playing Standard American. Betty's reasoning was that since partner didn't rebid diamonds, his diamonds must be short. Therefore she couldn't risk going to 4♦. Do you agree with her?

Let's think about what User123 has. First, could he have only 4 spades? It seems odd to compete to the 3 level with only a 4 card suit, but I suppose it is possible. If south only has 4 spades, diamonds is clearly a better fit than spades, so Betty should correct to diamonds even if User123's diamonds are short.

It is more likely that User123 has at least 5 spades, in which case playing in spades isn’t horrible. Except… if User123 has 5+ spades, why didn’t he open spades? Why would he open 1♦ with a 5 card major? The only reason is because south’s diamonds are even better than his spades. If this is the case, clearly diamonds is a better contract than spades.

So yes, Betty was correct that south didn’t explicitly promise longer diamonds, but had she thought through what partner could have to bid the way he did, she would have rebid the diamonds. This would have prevented a bad board for them (and the online recriminations that came afterwards in the chat window).