Overcalling is a contentious subject but to me there's five factors:
- Preemption
- Lead direction
- Playing strength
- Finding a sacrifice
- Risk
When deciding whether to overcall you balance the first four positives against the last one and decide whether it's worth it.
For example at favourable vulnerability:
♠ | 5 |
♥ | A T |
♦ | T 9 8 7 6 5 2 |
♣ | T 9 5 |
Pass - (1♣) - ?
This is a great time to stick a spanner in the works. 3
♦ is disruptive and may make it difficult for the opponents to find the right game or level. You're never getting doubled at these colours and with a passed partner you have free reign. You'd love partner raising to 5.
This time red against green:
♠ | A Q 2 |
♥ | Q J |
♦ | K 8 6 |
♣ | K 6 4 3 2 |
(Pass) - Pass - (1♠) - ?
Not this time. If there's a game available here partner will reopen and you have no suit worth bidding. You risk spending 500 points on a part score board or more against a game.
What about this one (nil vul)?
♠ | Q |
♥ | A 9 7 |
♦ | 7 6 5 3 |
♣ | A K T 6 5 |
(1♦) - Pass - (1♠) - ?
This time you have a nice suit in a reasonable hand; there's definitely a lead direction element here. But you don't have many tricks opposite a weak dummy. The only realistic game is 4
♥ and if partner can't bid at the one level that's not happening. There's no pre-emptive value and the risk of bidding in a live auction might be more than you think.
| ♠ | T 5 3 |
♥ | J 5 4 2 |
♦ | 9 4 2 |
♣ | 7 4 3 |
|
♠ | A |
♥ | K 8 |
♦ | A K J T 8 |
♣ | Q J 9 8 2 |
| | ♠ | K J 9 8 7 6 4 2 |
♥ | Q T 6 3 |
♦ | Q |
♣ | - |
|
| ♠ | Q |
♥ | A 9 7 |
♦ | 7 6 5 3 |
♣ | A K T 6 5 |
|
At the table opener is about to make a strong jump in clubs. They won't double you on this hand but I hope it demonstrates a point.
Would you (vul against not)?:
♠ | Q T 6 5 3 |
♥ | Q |
♦ | K 4 2 |
♣ | K 8 5 4 |
(1♥) - ?
What could go wrong at the 1 level? I've seen a couple of 1100s given out at the 1 level, lets not pretend there's no risk. There's definitely no pre-emption, no chance of a sacrifice at these colours and the lead direction very shaky.
The most likely contract is hearts to which you're on lead and into 3NT partner leading QT9x in a minor is likely to be much better than say 8x in spades.
Finally here's a hand from the Bowl (favourable vul):
♠ | 9 8 3 |
♥ | 6 5 4 |
♦ | T 9 |
♣ | A K T 9 4 |
Pass - (1♦) - ?
The risks shrink at this vul and the lead direction cannot be denied but the other virtues are questionable.
However, overcalling 2 minor over 1 minor can be devastating. Catch the opponents with a 54 major shape (do you double or bid the 5 card?) or a good pre-empt from partner and the auction gets very high before your opponents can evaluate their majors.
Linda Lee of bridge blogging has written up this particular hand
here.