1. To compete. With a good hand and/or a long suit the Overcaller wants to compete in the auction.
2. To sacrifice. With a weak hand and/or a good long suit, a preemptive overcall can lead to a worthwhile sacrifice.
3. To disrupt. Where the opposition are looking for a contract, an Overcall takes up valuable bidding space. Overcalling in Spades is especially disruptive because it forces the opposition to a higher level.
4. To indicate lead. With a strong suit but a weak hand, an Overcall can tell partner which suit to lead in defence. With an Ace and King in a 5 card suit but little chance of competing in the auction, an overcall can give a lead indicator for the defence. The opening lead in defence can defeat the contract.
For a Simple Overcall it is critical that the Overcaller has at least FIVE cards in the bid suit.
You need at least 8-15 HCP and one good Honour to Overcall at the One Level and 11-15 HCP and two Honours to Overcall at the Two Level. However the quality of your suit may be so good you can Overcall with fewer points.
Do the SQOT test - Number of cards in suit + Number of honours (10 is an honour for Overcalling)
A, K, 10, 3, 2 SQOT = 5+3= 8. You can overcall at 1 & 2 levels
K, 9, 8, 7, 6, 5 SQOT = 6+1 =7. You can overcall at 1 level only
SQOT - Suit Quality Overcall Test
If you have an Opening hand but your 5 cards are in Opener‘s suit you should PASS (“beware the silent man”). If partner Overcalls you might find a NT contract. Even if you have really good length and strength in Opener‘s suit, it’s nearly always best to pass.
You are looking for a fit in a Major. With 3 or more cards (A FIT) in the overcaller's suit, bid to the level of the fit.
5+3=8 Level of the fit is 2
5+4=9 Level of the fit is 3
5+5=10 Level of the fit is 4
With a fit you can count shortage points. Void +4, Singleton +3, Doubleton +2
Only change suits if you have fewer than 2 cards in the Overcaller’s suit, and an Overcalling suit (SQOT = 7+ for one level, 8+ for 2 level) of your own - ie at least 5+ cards of reasonable quality in your new suit. A change of suit here is not a forcing bid.
With no support, no biddable suit of your own and fewer than 9 points, PASS at the One Level
With fewer than 3 card support of Partner’s suit AND a stopper in Opener's suit
AND 9-12 HCP, bid 1NT in response to partner’s one level Overcall.
With 13-14 HCP bid 2NT.
With 15+ HCP bid 3NT.
If you have an Opening Hand but no 5 card suit, bid a TAKEOUT DOUBLE. This bid promises:
SUPPORT - at least 3 cards in each of the unbid suits (shows “tolerance”).
SHORTAGE 0/1/2 of Opposition’s Suit
Your partner MUST bid unless the Opposition intervene.
In fourth seat an Overcall can be more aggressive (you can ’borrow a king’ +3HCP). Responder has passed (0-5 HCP) so bidding here could help you find a fit or just by forcing Opener to bid again you could avoid letting them get away with a cheap contract. This is called a protective bid.
Sometimes you can make neither a Simple Overcall (no 5 card suit) nor a takeout double (no shortage in Opener’s suit) even with a good intermediate (10-15 HCP) balanced hand, so you must reluctantly PASS . You will have to settle for a good defensive hand.
However, If you you have a strong balanced hand (16-18 HCP), no 5 card major and one stop in opposition's suit, bid a 1NT OVERCALL. In fourth seat, you can make a 1NT Protective Bid with (about an Ace ) less - 11-14 HCP after 2 passes.
Responder to the 1NT Overcall can respond with ‘all systems on‘ (such Red Suit Transfers & Stamen if you play them) taking into account the points promised.
If you have 19+ HCP and are balanced, BID a TAKEOUT DOUBLE followed by NT at the lowest level.
If you have a weak hand (6-9 HCP) and at least 6 cards in a suit including 2 honours, bid a WEAK JUMP OVERCALL. This very descriptive preemptive bid disrupts opposition's bidding whilst giving the opportunity of a sacrifice contract if partner has a fit. A sacrifice contract is only worthwhile if opposition are vulnerable and you are not.
If an Overcall finds a fit, it can be a winning strategy in duplicate bridge, to bid the contract to one more than is likely to be achieved. This prevents opposition making part game.
If the Overcaller has 2 five card suits, she can use Unusual No Trumps (UNT).
With 0-9 HCP raise to the ‘Level of the Fit’ - Overcaller has at least 5 of a suit. Add the number of cards that you have in that suit and bid to that number of tricks. For example, if your partner bids a heart and you have 5 hearts the fit is 10(5+5), so bid 4H.
With 10+ HCP, and at least 3 of partners suit, bid oppositions suit at the lowest level - a Cue bid. The Overcaller will respond to the cue bid by rebidding the suit to to tell you his losing tricks. He will bid 2 of his suit if he has 8 losers, he will bid 3 with 7 losers, 4 with 6 losers. You agree the contract based on the number of losers in your hand.