A preemptive NT overcall of a major, shows a 2-suited hand with length in the lower two unbid suits. Some play this to show only the minors. Values depend upon agreement; the most common variation is for the bid to show either a weak (12 or fewer HCP) or strong (17+ HCP) hand. The Unusual NT may be 2NT or 1NT (if passed hand and partner hasn't bid) .
S: xxx H: xxx D: Axx C: Kxxx S: x H: xx D: QJTxx C: AQJxx W N E S 1S 2N 4S 5C X P/O Responses:
(a) Partner bids a known suit at the cheapest level to show a preference with no interesting in game.
(b) Partner makes a jump bid (e.g., 2nt pass 4c) to show good support. These bids tend to be preemptive. NT overcaller should continue to game only with very good values.
(c) Cue of the opponent's suit is a game or slam try, and is obviously one round forcing. If overcaller has a weak hand, choose the lower of the two suits. Any other bid shows a strong hand.
(d) A new suit not shown by partner (e.g., 1s 2nt pass 3H!) shows at least 6 in the suit, and is not forcing.
(e) 3nt is to play
(f) 4nt is Blackwood
Rebids By NoTrump Overcaller
(a) Bid or raise of a previously shown suit is natural and not-forcing. This shows a more extreme shape (6-5 or better).
(b) anything else other than a pass shows a strong suited hand (17+ HCP)
ADDITIONAL APPLICATIONS where Unusual Notrump is used frequently
(a) Over Strong Two-Bid - shows a weak two-suited hand. If the strong 2-Bid is natural, then shows the lower two unbid suits. If the strong bid is artificial (e.g., artificial 2C), then the bid shows both minors (Clubs haven't really been shown by opener).
(b) Over any NT bid, whether opening or response, shows lower two unbid suits (e.g., 1D pass 1nt 2nt! shows clubs and hearts)
(c) 2NT in balancing situation
(d) 3NT over a 2NT opening (this will always show a weak hand).
(e) UNUSUAL 4NT
(1) Over a 4S bid by opponents, 4NT is takeout for the unbid suit
(2) Over 4H, 4NT is takeout showing both minors.
(3) Over four of a minor, 4NT is Blackwood.
(4) Over any lower bid (e.g., 1h pass 3h 4NT) is takeout for the lower two unbid suits.
(5) If 4NT overcaller has previously bid a suit or doubled, and the opponents have bid at the 4 level, 4NT
(i) is takeout if the opponents have bid 4S
(ii) shows both minors if the opponents have bid 4H.