Judgement in OS

One main issue here is when to pass on borderline hands.
There are several hand types and situations with which it is advisable to pass:

• Borderline Power Double hands with length in opponent's suit and shortness in one or more other suits.
  For example: RHO opens 1S and you hold KJTxxx x AQx KJx. If we double, partner will probably run to hearts and we'll be stuck. If our spades and diamonds were reversed and RHO opened 1D, the situation would not be as clear, but we would still pass.
• Light overcalls in a four-card suit when partner is a passed hand
  Partner passes in first seat, RHO opens 1D and you hold xx QJTx KJxx Qxx. If partner were not a passed hand you would overcall 1H without a second thought. Now, however, the risks outweigh the advantages. You will probably not be able to compete effectively, since partner is weak, and is unlikely to have extreme heart length for his failure to preempt. And if you get doubled you have no place to go. If your suit were spades, an overcall would be slightly more advisable, since it has some small preemptive effect, but we would still pass. Similar considerations hold for Roman Jump Overcalls with minimum shape.
• Light 2-level overcalls
  We pass a lot more often than Fout's notes suggest. We overcall at the 2-level either with a standard 2-level overcall, or with a semi-sound preemptive hand (If opponents open 1S we do not overcall 2C with x Jx Qxx QTxxxxx, even though playing a standard competitive structure we might have overcalled 3C when non-vulnerable).

Once we do decide to overcall, there are a few areas where the requirements for different calls overlap. These are summarized below.

• Simple Overcall vs. RJO or Cue-bid:
  We almost always use an RJO. The only exception would be a 4-6 hand with a strong 6-card suit and a very weak 4-card suit, e.g. xxxx AKTxxx xx x. RHO opens 1m.
• Simple overcall vs. NTO:
  The only problem arises when we hold a 6-3-3-1 hand with shortness in RJO's suit. We tend to make a simple overcall with those hands unless
  • We hold a decent hand and the high-ranking suit or
  • We have a hand that is worth an IJO in strength, but the suit is not good enough.
  The reason for this is, of course, that using an NTO with, say, xxx AQTxxx KJx x may result in a silly contract if partner advances to 2S with 4-2 or 4-3 in the majors.
• NTO vs. RJO or Cue-bid:
  The overlap hands are 4-5-3-1 (or maybe 5-5-3-0) hands with shortness in RHO's suit. We almost always NTO. The exception would be a hand with extreme concentration in the long suits, especially if they are the majors. (Eg. AQxx KJTxx xxx x)
• RJO vs. IJO:
  We tend to RJO, except in cases of extreme concentration.
• NTO vs. PD:
  The problem hands are strong, fairly balanced hands with shortness in RHO's suit.
  • If we hold two cards in RHO's suit, we always use a PD.
  • If we hold a small singleton or void, we always NTO, then take strong action later.
  • If we hold a singleton honor, we use judgement based on hand texture, but we tend to NTO.
• NTO vs. IJO:
  We tend to IJO if the suit is good enough. See also the discussion above.
• NTO vs. 2N:
  With a strong 5-4-3-1 we tend to NTO, unless the 3-card fragment is very weak.
  With 5-5-3-0 we overcall 2N.
• IJO (or Namyats) vs. PD:
  We try to show our suit if at all possible. Our rules for Power Doubles include: no 6-card majors, and rare 6-card minors (notice that a strong overcall in a major is always possible, while the ones in the minors are sometimes taken up by the RJO's).
• 2N vs. PD:
  We tend to make a Power Double with less than 5-5, and at least two cards in RJO's suit, overcall 2N otherwise.
• 2N vs. IJO or Namyats:
  We lean towards showing the suit, but suit quality must be good.

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Constructive auctions in OS

The main advice here is "don't worry about it too much". The strength ranges are so wide that it is difficult to build a good constructive structure. You are trading precision with the ability to interfere in "the opponents'" auction. Most of the time you will just rely on the Law of Total Tricks for your bidding decisions. If you use OS also when vulnerable, you will need to pay more attention to constructive auctions. On the good side, your ranges, especially for Simple Overcalls and NTO's, will be narrower.
See Constructive Overcall Structure Auctions for more detailed suggestions.

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