What does “vulnerable” mean?

When you have scored a game, you are half-way to winning rubber and you become “vulnerable”. This means that when you fail in a contract, your opponents win 100 for each trick to go down by. When bidding vulnerable, you should be more cautious if you are bidding to spoil, expecting to fail. What is less well understood, however, is that you should be bolder when you think you might make game. For if you are vulnerable and make game, you have won Rubber (playing Chicago you get a 500 bonus for a vulnerable game as opposed to a 300 bonus for a non-vulnerable game so the reasoning is the same).

Exercise: vulnerable, you open 1 ♠ and partner bids 3 ♠. Would you bid 4 ♠ with these?

Answer: Yes with all three! Shapely fitting hands work out well even if the point count is not that great.

Moral: Bid up when vulnerable.