Responding to weak 2 openings

Weak 2 specification

In first and second seat you open the bidding with 5-10HCP, top 2 of 3 or 3 of 5 (counting the T as an honor), 6 cd suit, no 4 cd major side suit. This allows partner to try to find game optimally if possible. Note that it is between you and partner to consider if the "no 4 cd major suit" should be part of your agreeement - there are pros and cons and no clear plus or minus. This helps partner (who hasn't bid yet) to determine if a game is possible.

In third seat, you can relax the above criterion but be advised you should still have good honors in your suit. Its the same if you are considering a jump shift overcall of opponents opening bid. In both these cases, going to game is less likely so the criteria is relaxed (I sometimes even bid 3 level with 6 good cds as a jump shift overcall over opponent's opening).

Note that some 10HCP hands with 6 cds might be opened as a 1 level opener. e.g. a 10HCP hand that is 6043 : rule of 20 is achieved.

Responses

With about 15+HCP (or a good 14), you may want to start exploring for game. Rule of 17 is some times used and is good too. 

You might want to read this : https://www.larryco.com/bridge-articles/rule-of-17 

• A new suit (usually major) bid means responder has 5+ cds in the suit and wants to explore game in that suit. Opener bids 3 level or 4 level with support and min/max. A new minor suit should be bid with caution since opener has no way to arrive at NT.

• A 2NT is a feature ask. It asks opener "bid your side suit if you have a A or K in that suit and you are near a max 8-10HCP". Opener then bids

  • Repeats his suit if no inclination to go further (minimum hand)

  • Bid the side suit with a A or K (by promising top 2 of 3 or 3 of 5 in the long suit, he is effectively saying he is at max).

• With up to 12-13HCP, and a good fit (3+) for partner's suit, responder should consider using LOTT to raise his partner further (note that some 13HCP or even 12HCP hands, there might be a game to explore - see Larry Cohens remarks in the above reference). There's no likely game for the partnership, but you might frustrate a game contract by opponents (if you have a good fit, then opponents are likely short in your suit).

• Else pass.

For a stronger responder, a lack of a side suit AK might not matter too much - he might still go to game in a trump contract. 

If responder is considering a 3NT game, a side suit A or K is essential for entry to opener's hand (opener has most points concentrated in his 6cd suit), he also needs a stronger hand - say 16+HCP semi-balanced + a feature in his partner's hand. 

Example

The shape of openers hand can matter. Here's one example and it also uses the technique of visualisation.

Your partner opened 2S in first seat. You have 14HCP (a bit less than the guideline, but this is for illustration purpose and makes it more challenging 8-)).

1. You know your partner has 2 of 3 or 3 of 5 in spades. Since you have AJ, what's left is KQT. That makes it likely there are no losers in spades.

2. If you assume partner has 2 cards in each side suit (This is just an assumption for evaluation purpose), you can count a possible 2 losers in H, 0.5 loser in D, and possibly 2 losers in C (depending on where opponent A is). That's 4.5 losers. If I can cut down by one known loser, I might have a shot at game.

3. You bid 2NT (Feature ask). 

4. Partner will bid (A) 3S or (B) a side suit e.g. 3C, 3D, or 3H.

5. If (A), you let it go - partner probably has a minimum. You have a total of 9 spades anyway and might make based on LOTT.

6. If (B), 

   1. if 3C, that implies your partner has the AC and is near max. You may want to bid 4S. (your club suit will be your weak point. H suit is probably lost).

   2. If 3D, that implies your partner has the KD and is near max. You could potentially clear trumps and run the diamonds to discard at least one loser. But opponents might run H and/or C first. Game is probably not very likely (opps are likely to lead your weak suits). You may want to rebid 3S (or 4S if you need the win badly haha).

   3. if 3H, your partner is max but might have the K only. Not very good odds combined with your club suit. Rebid 3S.

Note that you might not need a AJ in spade suit to assume no losers in spades. This is a bit of overkill since you have 9 trumps between you. Just a K or KJ or KT or A might be enough (you must have confidence partner bid with top 2 of 3 or 3 of 5). The remaining honor points will go into your side suits.