When is the most advantageous times to intervene over an opposing preempt: with shortness in the opponent’s suit or with length?
Let’s take an example:
(2Spade Suit)  —  ?Hand 1: x, AJxxx, xx, KQTxxHand 2: xxxx, AJxxx, KQT, x

Hand 1 is a much better overcall for several reasons:

1. The shortness in RHO’s suit means that LHO is likely to raise. If LHO raises spades, you will have shown your hearts at the 3-level rather than trying to guess whether to show them at the 5-level.

2. The shortness means that your partner frequently will not have enough distribution to act in the balancing seat. Thus if someone is going to bid for your side, it needs to be you. On hand 2, if you pass 2Spade Suit, your partner will often be able to balance with a double and you will get a chance to show your hearts later.

3. Hand 1 has two possible strains. On Hand 2, if LHO doubles 3Heart Suit, you have no options.

The notion of stretching to overcall with shortness in RHO’s suits can sometimes be carried to extremes. For example:
(2Heart Suit)  —  ?
Hand: AQxxxx, –, xxx, QTxx

This hand can make a 2Spade Suit overcall. In fact, it would be dangerous not to bid!. If you pass, you could be shut out when the hand belongs to you for 4Spade Suit. Reverse the heart and club holdings, and now 2Spade Suit would be foolhardy. With QTxx of RHO’s suit, the imperative to bid is much smaller. When your side belongs in the auction, partner will often be able to double.

Now let’s switch positions: (2Heart Suit) — 2Spade Suit — (3Heart Suit) — ?

When should you expect full values for the overcall and when should you suspect he may have stretched? When you have length in hearts, partner has shortness and so may have bid on light values. But when you have shortness, expect partner to hold full values. Be cautious about doubling the opponents for penalty on a long weak trump holding–partner may not have many high cards.

So intervene aggressively with shortness. Be conservative with length. As Advancer, consider whether partner may have already overbid before bidding.

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