A disturbed double is:

  • Penalty if we have forced to game, or we have pre-empted, or if the scramble window has been open, or if we have already 'trained the guns' (see below); otherwise …
  • Takeout if the doubled bid is a natural suit bid; the takeout may be either two-suited or three-suited; otherwise …
  • Values, and where partner has already shown some values, it is train-the-guns i.e. subsequent doubles by either of you are for penalty.
WestNorthEastSouth
1123
dbl
Penalty: we are in a game force.
WestNorthEastSouth
23
dbl
Penalty: we pre-empted by opening 2.
WestNorthEastSouth
11
2pass22
dbl
Penalty: 2 opened the scramble window.
WestNorthEastSouth
12
dbl
Takeout, suggesting heart shortage.
WestNorthEastSouth
2
dbl
If 2 is a Multi, this shows defensive values, typically a weak no-trump.
WestNorthEastSouth
12NT
dbl
Whatever 2NT means, this is train-the-guns, asking partner to cooperate in expressing an opinion.
WestNorthEastSouth
3dbl3
dbl
You shouldn't take bids like 3 too seriously – it is often a lead director or just plain mischief-making on a hand that will scuttle back to clubs if the going gets tough. So treat double as train-the-guns, and 4 to play.
WestNorthEastSouth
1NT
dbl
A values double with as little as 12 points. A weak hand opposite may have to scramble with less than about 7 points, so minimum doubler should have at least two plausible places to play.

If a takeout doubler pulls partner's initial response to one of the other options, he is revealing his double to be two-suited. If he makes the cheapest such bid, it is not forcing; otherwise it is.

WestNorthEastSouth
3
dblpass3pass
3
Forcing, showing a strong major two-suiter. 3 instead would have been non-forcing, offering a choice of 3 and 3 as the final contract.

When it is no longer rational for a double to be takeout or values, then it is usually penalty or lead-directing. But a late double of a freely bid 3NT or slam is for a club lead.

NEXT: disturbed pass