Source: Ask Jerry
Dear Jerry: Could you clarify the difference between ‘offensive’ and ‘defensive’ values? —W. Arnold Charlotte, NC
Dear W.A.: Offensive values are cards you expect to take tricks if your side is declaring … playing tricks. Defensive values are cards you expect to take tricks if your side is defending. Compare these two hands:
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The first has excellent offensive values if your side is declaring with hearts as trumps. You are sure to get five winners, even if partner is short in hearts with no useful high cards. It has little defensive value. Suppose the opponents are in a spade contract. If they have the 
A, you may take no tricks. Even if they don’t have a singleton heart, declarer may be able to discard any losers on other winners.
This is a good hand to make an offensive bid: a weak two-bid or a weak jump overcall if the opponents open. You have lots of playing tricks but little or no defense.
The second hand has much less offensive value, even with hearts as trumps. You’ll get a trick with the 
A and at least one heart trick, but it’s unclear that you’ll get much more if partner doesn’t have a good fit and some high cards.
On defense, the hand has good prospects. If the opponents get to 4, for example, you have a sure trick with the A and may get a second with the J. You might get a trick with the K and even the 
Q may take a trick if declarer has to try a finesse in the suit.
The second hand is not a good opening bid, even at the one level. It would also not be a good overcall. Pass and await developments.
A hand’s offensive strength can prompt you to bid with very few high card points. Suppose partner opens 2 and this is your hand: 6 7 6 4 3 9 8 6 3 
8 7 5 4.
The suggested bid is 4! Look at what happens if partner has the first hand. Partner takes five heart tricks and can trump two spades in dummy for a total of seven tricks on offense. On defense, there are no tricks. The defenders have only
three hearts, including the yA. They can make a grand slam. You’d rather play the hand than defend.