An add-on or a throw-in is any card discarded to your opponent with the full knowledge that it is a card that can be used by him to be added on to an existing meld. That is, if you know your opponent is holding a meld of three 10’s and you discard the fourth 10, this discard is considered to be an add-on.
Add-ons frequently have an offensive value in the fact that they permit you to play the full value of your hand rather than destroying some of your offensive strength in order to hold those cards that are wanted by your opponent. There are many occasions when an add-on to your opponent will, if picked, reduce his hand only by the value of the one additional card that he is free to discard. Whereas the discarding of a total wild card may reduce his hand by as much as 20 points, depending on what he needs. Your opponent may be able to meld two other cards to that one wild card that you discard to him.
Most of the questions related to when or when not to add-on occur in the later stages of play. Frequently it comes up under the following circumstances: You are holding nine melded cards, plus what appears to be a completely wild card. You have no indication as to whether your opponent specifically needs the card or not. However, it does represent a card that has been missing from play. If you draw from the deck a card that definitely fits your opponent’s run as an add-on, the question then becomes whether you should throw the add-on or not.
There are specific occasions when you will not have any logical determining factor as to whether or not it is best to add-on to your opponent, and at this point it must be realized that the throwing of an add-on will be a calculated risk. The calculation of this risk must then be based entirely on the mathematical probabilities and odds of the advantage that can be given to you by the throwing of this card and getting away with it. This needs to be compared to the disadvantage and potential loss to you in throwing the card and not getting away with it. In other words, the answer to the question of whether or not to throw an add-on or not depends on two basic factors:
1. Knowledge of your opponent’s cards that he is holding
If you know that an add-on will gin your opponent then you should throw the wild card and hope for the best. Under most circumstances, an add-on will be considered a wise throw. Add-ons can be extremely beneficial if used in the write way. It also can be very costly if the luck doesn’t exactly work out for you, but you should try anyhow.