[gprentice]

At my club at match-points (not IMPs) with this hand, 5 people played in 3D by west, 6 people played in 4D by west, 4 people played in 3S by north. 3 spades going 2 light was better for east west than making four diamonds.
I can't remember the actual bidding but after 3S by north, how does west judge whether to bid 4 diamonds or not. I realise that bidding 4D when vulnerable is definitely wrong but what about when west is not vulnerable. If 3S makes and 4D goes 1 light (even doubled), it's better than letting north make 3 spades. How should west decide whether to bid 4D or not?
Also should north double 4D? At my club, one pair played in 4D doubled making and top board.

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[mw64ahw]

a) if South is prepared to bid after a pass then maybe it is better to have a structure that caters for an immediate pre-emptive bid. E.g. 1♠-2♠ as pre-emptive, with 1♠-2♥ as constructive+ or GF 5+♦ a la Ambra
b) West has a hand that should almost be comfortable playing at the 3-level. Once South has passed and ♦ support has been shown a raise to 4♦ is warranted even vulnerable for me.
c) South has nothing so North has to be sure of enough tricks in their own hand to X. I can only count 3 if ♠ split evenly.

[helene_t]

IMHO West should double 3♠ instead of bidding 4♦. West's hand is quite defense oriented and they have only five diamonds.

But E might pull to 4♦ anyway so it might not matter.

The rest of the auction is fine, IMHO.

[AL78]

gprentice, on 2024-July-03, 17:24, said:

I can't remember the actual bidding but after 3S by north, how does west judge whether to bid 4 diamonds or not.

At my club it comes down to how lucky you are, how bad you are at defence and/or how much you hate defending. The latter motivates you to buy as many hands as possible, the former makes it very likely you won't be punished in the process even when it is theoretically unsound.

[P_Marlowe]

The usual answer is rarely.

A common short cut is provided by the Law of Total Tricks, how many trumps you have,
how many do they have.
It is quite often reasonable to assume 9 trumps each, this means 18 total tricks,
if 4D makes, 3S is down 1, if 3S makes, 4D is down 2.
Playing MP, being red this translates to almost never, being green, this may depend
on how likely they are going to double you, ..., and sometimes they have underbid and
will bid (making) 4S over your 4D.

[akwoo]

The important rule of thumb to remember is the Law of Total Tricks. It says:

(The number of tricks you take in your contract + the number of tricks they take in their contract) = (the number of trumps you have in your fit + the number of trumps they have in their fit).

Here, you expect opponents to have 9 spades (opener with 6 to rebid 2S and responder with 3 to raise to 3S) though they could have 10 or, on an aggressive day, 8.

You expect to have 8 or 9 diamonds (partner's raise doesn't promise 4, and partner would usually jump to 4D with 5).

That makes for a total of 17-19 total tricks.

At matchpoints, my rule of thumb is that you should bid if it's very unlikely for both contracts to go down. Here, it's quite possible for both 3S (9 tricks) and 4D (10 tricks) to go down, since there might be only 17 total tricks.

Hence you should not bid over 3S. At matchpoints, you might risk a double, which shows extras without the ability to bid 4D on total tricks.

The law of total tricks isn't always right, and there are some relatively easy adjustments to make it somewhat more accurate, but it'll get you to a correct decision more often than not.