How many errors can GIB make on one hand?

The other day, I was playing one of those 25 cent all-day tournaments on BBO (IMPs). On the last hand (none vulnerable), my GIB partner picked up the following hand: ♠5 ♥J875 ♦96 ♣AK8763. RHO dealt and passed, as did GIB. LHO opened 1♠ and partner overcalled 2♦. RHO now raised the stakes with 2♠. You have some useful looking values. What do you call?

Double (technically a "responsive" double here, but I'm treating it as just another competitive double) would suggest sufficient points for it to be our hand, four hearts and four clubs (maybe five if the suit is not headed by good honors). The other four or five cards should be one or two diamonds (else why not raise?), and two--possibly three--spades. In other words, a relatively balanced hand with both the round suits, and about 10 or more points.

Why do I say at least two spades? Because experience has taught me that when you are short in the opponents trump suit, if partner leaves it in, those little trumps that you do not have will be in declarer's (or dummy's) hand. And it's slightly more more likely that partner will have four and leave it in with the hope that the opponents are on a seven- (or at most eight-) card fit.

And why should you have the balance of power? Because whether you choose to play in a possibly poor trump fit, or to defend a doubled contract of the opponents', you need to have some reasonable expectation of making or setting them, as the case may be. This is especially true at IMPs where an injudicious contract our way can get doubled and go for quite a number, or where doubling their part-score into game could be very expensive. You should aim to have at least 22 hcp between your two hands if you're forcing partner to bid at the three level (or defend). In this case, we can assume partner has 12 hcp (he did make a 2/1 overcall) so we should have 10.

Here, we have too few hcp (eight) and too few spades (singleton). Not a hand to double, therefore.

What about 3♣? Well, if you do bid here, you should have a good honor sequence so that partner's lead of your suit (if we end up defending) isn't an instant own goal. And, you should have at least a decent five-card suit with some tolerance for partner's suit in case he has to go back to his suit. 3♣ would be the perfect bid here! You have the very best possible lead-directional suit, headed by AK. And a doubleton diamond on the side.

Eschewing the obvious 3♣ bid (you don't want to miss a 4-4 heart fit!) you double and partner, trusting your judgment, passes. It's unfortunate because 5♣ our way is cold (partner has Qxx and they split 2-2). Partner leads a trump, not his diamonds. What do you deduce from that? Possibly a broken suit, so the hand has scattered honors. After drawing trumps, declarer starts to eliminate clubs. You win and lead your ♦9 covered by ten, jack, ace. A second club comes which you win and now there's one obvious card in your hand that will set the contract--your other diamond. But being the GIB, you don't worry about partner getting endplayed and you lead a heart. Game over.