Making the right defensive decision in a game of gin rummy comes down to the basics of knowing how to do so. There are certainly right and wrong decisions to be make, and to become an expert player at this game, you need to learn when and how to do this.
An example of a wise defensive play is to utilize the full offensive value of lay-offs against an opponent. When playing against a player who is primarily a knocker or who is forced by a score situation to knock his hand quickly, you need to keep in mind that the lay-ff cards are of no value in your hand until such time when your opponent knocks. There are also occasions when an opponent who is doubtful or hesitant in knocking can be forced to knock by your discarding a fourth card from one of your runs. This action on your part gives the impression that you are in trouble with your hand. You are then in a position to underknock him by retaining the lay-offs you have in your hand.
Another important consideration in defensive play is the relative value a discard represents to your opponent. That is, can the discarded card give the opponent only a three-card meld, or a four card meld, or more importantly, does the card allow him to tie up in a meld any cards that he is holding against you? The latter is the one type of throw that is strictly avoided by all skillful players concentrating on defense.
In playing defensively it is extremely important to build melds around the cards that you are forced to hold against your opponent. For example, if you have given an opponent the 7♦, 8♦, and 9♦ sequence, and you now pick the 10♦, you are forced to hold the card. At this point you should try if possible to obtain the other 10’s or try to buy the J♦ and Q♦ so that the card you must retain for defensive purposes is also put to an offensive purpose. In fact, the building of your hand around the opponent’s need cards is the ideal manner in which to defend a hand. You need to remember that any gin player can hold up defensive cards accidentally, but only an expert player will hold up these cards purposely and at the same time build a winning hand around them. In order to accomplish this, you need to have patience since this is the determining factor as it requires ample time to set up such a hand. Therefore, you should only do this if you are in a must-gin situation, or when there is a low knock card.
In many cases, the best defense against an opponent is a knock, in spite of the status of the score or any other factor. In the late stages of a game you need to be aware that your opponent can go gin or knock at any given time, and you need to be proactive in avoiding that.