Safety Plays at Teams vs Pairs
At teams, give up an overtrick to protect the contract. At pairs, the same insurance often costs more than it saves.
A safety play gives up a likely overtrick to protect against a bad split. Whether that is a good deal depends on how the game is scored.
Why it works
Teams (IMPs): a non-vulnerable 3NT making scores +400 and an overtrick adds just 30, worth about 1 IMP. Going one down scores −50, a swing of 450, about 10 IMPs. A small chance of losing the contract outweighs a large chance of an overtrick.
Pairs (matchpoints): you are compared with the other pairs playing the same cards. An extra 30 points can beat every pair who made exactly nine tricks. Every board is worth the same, so a line that gains an overtrick most of the time can be right even if it occasionally costs the contract.
A worked example
You are in 3NT with five sure tricks outside diamonds. Dummy's only entries are in diamonds.
Dummy (North): ♦ A K 6 5 4 3
Declarer (South): ♦ 7 2
You need four diamond tricks for the contract.
Safety play: duck the first diamond. You still have a diamond to lead to the A K. If diamonds split 3-2, you make five diamond tricks. If they split 4-1, you lose a second diamond but still make four. Either way the contract is safe.
Play for the maximum: cash the A K. If diamonds are 3-2 (about 68%), all six diamonds win: an overtrick on top of the ducking line. If they are 4-1, you lose the third round with no way back to dummy, take only two diamond tricks and go down.
At teams, duck: the contract matters far more than the overtrick. At pairs, if most of the room is in 3NT, cashing gives you the better score about two times in three.
Four common mistakes
Using safety plays at pairs out of habit when everyone else will make the overtrick.
Ignoring safety plays at teams in order to make an overtrick.
Forgetting that at pairs an unusual contract changes the maths.
Not counting your sure tricks before deciding.
When the rule does not apply
At pairs, take the safety play when you are in a good contract that the rest of the room may miss, because just making it is already a good score. Also take it when the danger case is more likely than usual, for example after a pre-empt. At teams, don't take a safety play that puts the contract at risk in a different way.
Key takeaways
At teams, protect the contract.
At pairs, compare yourself with the rest of the room.
Work out what the safety play costs and how often.
An unusual contract at pairs changes the decision.