Natural 1NT overcall

Wbridge5 has three natural 1NT overcalls of a 1-of-a-suit opening. The seat and whether the overcaller has passed decide which one it is.

A passed hand’s direct 1NT is unusual, not one of these. In the balancing seat a passed hand’s 1NT is natural again.

The balancing ranges come from probing Wbridge5 5.12. Over (1♥) P (P), balanced hands with 12–14 HCP bid 1NT and those with 15+ HCP mostly double. Only 2 of the 17 hands with 15 HCP bid 1NT. The range is the same over (1♣), (1♦) and (1♠). Over the minors, balanced hands with 12–14 HCP and no 5-card major bid 1NT on 86 of 144 boards and otherwise doubled, passed or bid a suit, and 7 of 35 balanced hands with 15 HCP bid 1NT over the three openings. When the balancer has passed before, it bids 1NT with 10–11 HCP.

After every one of these overcalls, the advancer plays systems on. Its calls are the responses to a 1NT opening, with Stayman and transfers. The changes come from the adverse suit and from the overcaller’s range.

The probes were run with no one vulnerable. Advancer held 0–16 HCP. Ranges here are in HCP.

Advancing the direct 1NT

Over (1♣♦)

The probes dealt the same hands to the advancer and to a responder after 1NT - (P). Over (1♣), advancer made the same call on 265 of 283 hands, and over (1♦) on 264 of 283. Wbridge5 drops the transfer into the adverse minor.

A weak hand with 6+ cards in the adverse minor passes, e.g. ♠A75 ♥7 ♦874 ♣QJ6532 over (1♣) and ♠86 ♥2 ♦Q108753 ♣QJ53 over (1♦). The second hand transfers with 3♣ over (1♥). Stronger hands with the adverse minor bid 2NT or 3NT.

Over (1♥♠)

Over a major, advancer made the same call as a 1NT responder on 191 (1♥) and 199 (1♠) of 283 hands. Most changes come from holding length in the adverse major.

Other calls are as over a 1NT opening, e.g. 2♠ for clubs and 4♠ for the minors.

• Stayman asks only for the other major. Without 4 cards in it, advancer bids 2NT or 3NT, even with 4 cards in the adverse major. Over (1♥), ♠73 ♥AJ75 ♦J1062 ♣AJ6 bids 3NT and ♠Q3 ♥Q982 ♦A10983 ♣74 bids 2NT. After a 1NT opening, both bid 2♣.
• No transfer to the adverse major. A weak hand with 5+ cards in it passes, e.g. ♠86 ♥A10653 ♦K965 ♣103 over (1♥). A better one bids 2NT or 3NT: over (1♠), ♠Q10964 ♥AQ10 ♦6 ♣10743 bids 3NT.
• 5-5 majors transfer to the other major, e.g. ♠AJ862 ♥KQ942 ♦4 ♣92 bids 2♥ over (1♥) and 2♦ over (1♠). After a 1NT opening this hand bids 4♦.
• The jump cuebid shows a 3-suiter short in the adverse major. It is rare (2 boards over (1♥), 3 over (1♠)), 8–15 HCP, e.g. ♠K1093 ♥A ♦K874 ♣KQ62 bids 3♥.

The bid just below the adverse major, (1♥) 2♦ or (1♠) 2♥, is natural. Advancer almost never makes it: 2 of 300 boards with 5+♥ over (1♥) and 2 of 300 with 5+♠ over (1♠). Each of those hands has 5 cards in the adverse major and a 6-card minor. The overcaller always reads it as natural (below).

Overcaller’s rebids

When Wbridge5 overcalls 1NT itself, it answers advancer as a 1NT opener does, with two changes:

• Stayman asks for the other major only.
• The bid just below the adverse major is a natural sign-off.

For example, ♠J5 ♥AK63 ♦KQ108 ♣K96 answers 2♦ over Stayman after (1♥). ♠KQJ ♥1082 ♦K542 ♣AKJ bids 2NT over 2♥, and ♠AJ98 ♥A5 ♦K65 ♣A764 bids 3♠. These answers fit the transfer rebids.

Responder raises: (1♥) 1NT (2♥)

When responder raises the adverse suit, advancer bids as after 1NT (2♥), with one exception: it never doubles. The probe dealt the same hands to both auctions. Advancer made the same call on 237 of 283, and none of the 300 boards drew a double. The hands that make a cooperative double after 1NT (2♥) bid 3NT, 2NT or pass instead. For example, ♠KQ4 ♥842 ♦1093 ♣AJ72 bids 3NT and ♠8732 ♥96 ♦K85 ♣KQJ7 bids 2NT.

Advancing a balancing 1NT

After (1♥) P (P) 1NT (P), advancer has passed over the opening. It keeps the 1NT system but needs about 2 HCP more than over a direct 1NT. On the same hands as over a direct (1♥) 1NT, it passed 82 hands that would have bid there.

Balanced hands usually pass with 9–10 HCP and bid at 11 HCP. For example, ♠KQ4 ♥842 ♦1093 ♣AJ72 passes, though it bids 3NT over the direct overcall. ♠A1053 ♥J1052 ♦A2 ♣K74 bids 2♣.

The jump shifts are takeout jump shifts, as for a passed responder. For example, ♠— ♥Q732 ♦A10762 ♣Q1082 bids 3♠.

After a passed hand’s balancing 1NT

After P (1♥) P (P) 1NT (P), advancer has also passed over the opening, and partner’s 1NT shows only 10–11 HCP. The thresholds rise again. The probe dealt advancer at most 12 HCP.

Compared with the unpassed balancing 1NT, 11–12 HCP hands invite instead of bidding game: ♠73 ♥AJ75 ♦J1062 ♣AJ6 bids 2NT here and 3NT there.

Not probed

• Stoppers in the adverse suit. The harness constrains only suit lengths. The probed overcallers held 3–4 cards in it.
• Advancer’s second round, e.g. after a Stayman answer or an acceptance.
• Overcaller’s rebids after the balancing 1NTs.
• Advancer with 17+ HCP: the 4NT and 6NT ranges stop at the probe’s 16 HCP cap.
• Overcaller’s answer to 2NT over (1♥) 1NT (2♥).
• Interference other than (1♥) 1NT (2♥), e.g. a double or a new suit.
• Advancing a balancing 1NT over openings other than (1♥), and a passed hand’s balancing 1NT over them.