2-Level (Non-Jump) Overcalls
Overcall Bid Order Numbers
Responses To Overcalls:
Raising Partner's Overcall Other Bids
"Impossible" 4th-Seat Holdings
Overcall Response Bid Order Numbers
Fourth Seat Overcalls
A 2-level overcall (such as 1-2) requires close to opening strength and a good 5-card or longer suit. With a stronger hand (a good 14+ HCPs), BidBase will overcall with a poor 5-card suit (e.g.: QT654).
Would you overcall 1 with QJT87 QT7 54 AQ5? It has a Spade suit that might only take 2 tricks (if LHO has AK92 or more). The other Queens may not be worth anything, leaving this hand with possibly only 3 tricks.
However, as the bidding simulation Poor_1S_suit_overcall.sim shows, there is only a 9% chance of overcaller's LHO having AKx or more. Meanwhile, there is a 66% chance that overcaller's partner will have 3+ Spades and a 42% chance that he will also have 3+ HCPs in Spades, making this overcall of the boss suit a pretty good bet, particularly if RHO is opening in 4th seat after 3 passes.
Over RHO's 1, Lawrence suggests overcalling 1 with almost any 5 cards so as to block LHO's 1 bid.
Illustrative hands given by Lawrence:
On the last hand, if LHO has 3+ HCPs in Spades, that means he has the Ace and another honor over your King. Running a sim to look for that situation found that LHO will have AQJ, AQx or AJx or more in Spades 26% of the time. Partner will have 3+ card support for Spades 66% of the time, just as before, but will have also have 3+ HCPs in Spades only 35% of the time.
Although this is not as good as the previous hand we simmed, it still looks like good odds. (See Poorer_1S_suit_overcall.sim.)
Overcalling 4-card suits:
In his column Aces On Bridge, Bobby Wolff says to bid 1 with AKQ6 J7 876 K543. In his book Takeout Doubles, Mike Lawrence says to double with similar hands, but on page 8 of his book, Overcalls, Lawrence says to overcall with a strong 4-card suit such as AKQ9 872 Q43 T97. But he says to do this only at matchpoints, not IMPs.
But then Lawrence goes on to say that you can also overcall 1 with Q987 87642 KJ3 A over RHO's 1 opening because your length in Hearts means that partner is probably short in them and thus more likely to have support for your Spades, though this is "risky at matchpoints and insane at IMPs".
Originally, we went along with this reasoning and made entries for overcalling with a poor 4-card suit when holding 5 of RHO's suit, but a discussion on rec.games.bridge changed our minds.
To verify the numbers in the discussion, we ran a sim on overcalling with 2 of RHO's suit versus with 5 and got almost identical numbers. Either way, after 1 by RHO and overcaller holding 4 Spades and assorted other cards, overcaller's partner will have less than 3 Spades around 25% of the time, exactly 3 Spades about 31%, 4 Spades about 26%, and more than 4 Spades about 17% of the time.
As a result, we have left in the entries with overcalls of very good 4-card suits, despite some serious reservations about them, but 0-ed out those with lesser 4-card suits, no matter what the holding in RHO's suit.
And just like opening preempts, jump overcalls can be very sound, very weak, or anything in between. Sound preempts of old were based on having enough tricks in hand (not counting on partner for anything) to not go down more than 3 tricks at favorable vulnerability, 2 tricks equal vulnerability, and 1 trick unfavorable.
Today's thinking is to allow for partner having a little something, so light preempts are dependent more on suit quality, distribution, and vulnerability. When vulnerable, you should have a nearly solid suit (missing one honor) or longer suit and non-vulnerable, most experts will preempt with total garbage. In neither case should you have much outside your suit, nor should your suit be headed by the AKQ because in either case, you may be missing 3N when partner has a little something.Unusual Notrump.
A 1N overcall normally is natural and shows 15-18 HCPs (per Bidding Dictionary), but if overcaller is a passed hand, he cannot have 15-18 HCPs, so 1N is treated as an Unusual Notrump.
Responses To Overcalls
If you want a jump raise to be a limit raise (4+ cards, 10-12 points), activate that entry (Bid Order #310000) and deactivate the preemptive entries (#430000, 431000, 432000, though just deactivating one of these entries will deactivate all entries with names of Overcall: Raise, Preemptive).
Beware of a hand like T98 K983 KQ42 85 on bidding of (1)-1-(1N) because RHO's 1N bid not only shows some values, but it shows some Spade honors which are on top of partner's. (More on this below.) Also, your length in LHO's suit may mean that both partner and RHO are short, leaving RHO able to overruff partner.
A hand like K983 85 T98 KQ42 is much better on the same bidding because you have a high Spade honor plus intermediate over RHO's Spades, plus you are shorter in LHO's suit, not to mention the extra trump for partner.
In SAYC, when overcaller responds to a cue bid, he must rebid the same suit with a minimum 8-11 HCPs (and thus a rebid does not promise extra length). Any other bid promises 12-16 HPCs.
In Overcalls, page 73, Lawrence shows Q652 KQJT7 3 KQ7 and says to jump straight to 4 after 1-1-P. However, cue-bidding or a splinter raise allows partner to explore for slam.
Like most of SAYC, the above methods have the benefit of simplicity at a cost of being able to show more about your hands.
Here is a non-SAYC response structure (after, for example, (1)-1-(P)).
This structure applies only when RHO's bid, if any, is not higher than 2 of LHO's suit. For example, after 1C-1S-2H, you would have to bid on the 3 level to cue bid, and that is too high to bid for an 8-10 HCP, 3-card raise.
For competitive purposes, we really prefer these methods (though BidBase's default is SAYC), but note that if you play them, there is no way to show a balanced or semi-balanced 13+ HCP hand with 3 or 4+ trump support, such as KQx AQxx xx Kxxx, after bidding like (1)-1-(D).
We ran a sim to see how often this type of hand comes up, and the answer was 3% of the time on bidding of (1)-1-(P) -- not very often, but what are you going to do when that 3% does come up? One idea is to cue bid 2 to show 3 Spades or 3 to show 4+, then if overcaller corrects back to Spades (showing a minimum), raise Spades with 13-15 HCPs or cue bid again with more HCPs.
Beware RHO's 1N: if partner overcalls and your RHO bids 1N, he is advertising honor(s) in overcaller's suit, as well as some values. As Mike Lawrence points out in Overcalls, you should be cautious of raising with a minimum, especially without any trump honors of your own. (My favorite line of Lawrence's: When you overcall aggressively, you give the opponents problems. here, RHO seems to have solved the problems.)
Whether or not to raise over 1N is not a matter of HCPs, but of trump honors plus distribution. After (1)-1-(1N), you can bid 2 with KJ87 5432 5432 2, but you should pass with 872-K7654-KJ2-32, and bid only 2 with a hand with which you might otherwise bid more, such as Q8543 KQ2 A32 32. With 3 small and shortness in opener's suit plus a quick trick or two, such as 842 AK432 5432 2, you can still raise since your RHO will likely lead opener's suit, setting up your ruffs.
If RHO doubles: A Negative Double might show a good hand, but it might also be a hand with a good 6+ suit, but without the points to make a 2-level bid, so RHO doubles first, then bids his suit. Thus, when RHO doubles, he may be strong, but he may also be weak. When you are strong, he is most likely weak.
If the bidding goes 1-1-D and you have something like KQ7 KQ84 J7 J874, you do not have an easy bid. The hand is too strong (12 HCPs) for a simple raise, and lacks the 4-card support promised by a limit raise.
If a new suit bid were forcing, you could bid 2 and then raise Spades later, but SAYC is silent on whether a new suit is forcing, and BidBase goes with Mike Lawrence on making a new suit bid non-forcing.
Fortunately, SAYC uses a cue bid as a general forcing bid, so we can cue bid with the above hand and then raise Spades.
Note that this cue bid does not promise support for partner's suit. Advancer could have a hand like 82 KQ4 J7 KQJ874.
If RHO bids 2/1: Unless the opponents are playing Negative Free Bids, RHO shows at least a good 10+ HCPs by making a free bid on the 2 level. This means that your side should not half the points in the deck, much less enough for game (except on freak distributional hands).
This would seem an ideal time for preemptive bids based on trump length, a la the Law Of Total Tricks. However, Mike Lawrence, on whose work we base many of our entries, doesn't seem to believe in LOTT. (See his book: I Fought The Law....) In this situation, we are departing from ML's advice and going with LOTT.
If you prefer ML's view, you will need to change the entries. For example, ML will raise to only 2S with 4-card support after 1C-1S-2H while BidBase raises to 3S per LOTT.
Normally, when partner has overcalled with a major and you have support for him, you should raise him rather than bidding your own suit.
However, when the bidding goes 1-1-P and you have a good major suit, especially one which you would like partner to lead if you end up on defense, then it is right to bid your suit even if you have 3-card support for partner. Of course, the drawback is that if the bidding gets too high before your turn to bid again and if partner doesn't have your suit, you've lost the chance to show your support.
With no support for overcaller's suit, advancer can bid:
To jump in a new suit: Bidding Dictionary (Truscott) says that a jump shows 10-14 HCPs and a long, strong suit, which is what BidBase defaults to in SAYC. Truscott says that a jump can be played as either non-forcing or a one-round force, depending on partnership agreement.
Mike Lawrence says in Overcalls (p. 72) that a jump shows a good 13 to a poorish 15 and may be a very good 5-card suit. ML says that a jump is non-forcing. If you prefer ML's version, change BidBase accordingly.
Incidentally, a strong jump assumes RHO has passed (e.g.: 1-1-P. If RHO has bid, then you can't have even 10 HCPs unless someone else has lied.
Mike Lawrence says that he would lean towards 2NT with J7652 Q2 AK8 KT7, despite the 5 Spades because 1 would not be forcing, the suit is not good enough for 2, and 2NT shows the points. However, this hand evaluates as only 11 KNR points, so it isn't all that strong. We stay with 1.
If advancer's RHO makes a takeout double, he usually has 4+ cards in the unbid suits. For example, after 1-1, a Double normally shows 4-4 or even 4-5 in the majors. For you to bid one of those suits, you probably should upgrade the requirements from any 5-bagger to a decent 6-card suit.
If advancer's RHO makes a 1-level bid, such as (1)-1-(1), he could have as few as 5 or 6 HCPs. When he makes a 2-level bid, such as (1)-1-(2), he normally has a minimum of a good 10 HCPs, and you should be much more cautious in bidding a new suit on the 2 level. The best time to bid 2 of a suit is after RHO has passed or raised opener, showing some weakness.
Along the same lines -- many people play Inverted Minors, in which case a jump raise of a minor is weak and a single raise is strong. In the database, we are aggressive against weak single raises and cautious over strong single raises.
First of all, it is possible that someone (hopefully opener and not your partner) has psyched. Secondly, it is barely possible that LHO opened with a distributional 10 HCPs, partner overcalled with a distributional 5 HCPs, and RHO bid on the 2 level with 11 HCPs, leaving 14 HCPs for you.
When RHO bids 1-over-1 and you can overcall on the 1 level, you should do so only with a good hand and/or a good suit. Partner may have had to pass in 2nd seat without good shape, but could still have some points, and a 1-over-1 by RHO could be based on shape and few points, so there is still a chance the deal could be yours.
When RHO bids 1-over-1 and you have to overcall on the 2 level, again, the deal may still be yours, but you need to have a shade better hand/suit to bid overcall one level higher. There is some danger because RHO has not limited his hand yet.
When RHO bids 1N, he has limited his HCPs and he has limited his length in LHO's suit and higher suits, making it safer for you to overcall in those suits. You should bid more freely than in the previous cases.
When RHO bids 2-over-1, the stronger your hand is, the more likely that your partner has nothing. You may have to pass a 17-HCP hand and overcall with an 8-HCP hand. An overcall must be based on shape - in particular, a quality suit and length in RHO's suit -- making it more likely that your partner is short in that suit and  is more likely to have a fit for you and  will be able to overruff LHO in that suit.
When RHO raises to the 2 level, then as with his 1N response, he has limited his HCPs and his holdings in higher suit. So again, you can overcall freely in those suits.
The Location Of Honors:
On page 23, ML shows two similar hands: Axx KJx KQJxx 54 and KJx Axx KQJxx 54, the only difference being that the major suits have been swapped. The bidding has gone (1)-P-(1). If you study the hands, it is obvious that the KJ are weak in the first hand because the Heart bidder is on your left, while they are worth a lot more in the second hand as Spades because the Spade bidder is on your right.
ML says that the first hand is a stretch (non-vulnerable) at matchpoints and only worthy of a pass at IMPs, but that the second hand is always worth a bid.
We ran a simulation of 20 million deals and the results agreed with ML's recommendations. But the sim also shows that 67% of the time, you will have an 8-card or longer Diamond fit, so we think that a non-vulnerable bid is protected by the Law of Total Tricks, even at IMPs. At the 3-level, there is a 33% chance that you will have a 9-card or longer Diamond fit, while there is only a 5% chance of a 9-card fit in either major for the opponents, actually giving you the advantage if bidding gets to the 3 level.