The discard window
The discard window is the position in the round where the right move is to throw a card you can use, in order to deny the table a card they need. Most beginners throw only the cards they cannot use. Experienced players throw the card that is the most expensive to the table.
The two-player table
At a two-player table the discard window is sharp. You and your opponent are reading each other's hand through the discard pile. Every card you throw is a signal. A throw of a high-probability card (an 8 in the middle suits, a wildcard joker) is a strong signal that you have closed your meld. A throw of a low-probability card (a 2 or an ace, a suit card you do not need) is a weaker signal.
The four-player table
At a four-player table the discard window is wider. You are reading three opponents, not one. The signal-to-noise ratio of a single throw is lower. The discard discipline is the same, but the read takes longer. The recommended tempo at a four-player table is slower than at a two-player table, not faster.
The math of the discard window
Before each discard, count the cards in the closed pile that complete each of your open sequences. If a sequence can be completed by a single card and that card is unlikely to be drawn by the table, the sequence is safe. If a sequence can be completed by several cards, throwing the cards that close those sequences is the right move.
The "expensive" card
The most expensive card in the discard pile is the card that completes three of your opponents' open sequences. That is the card to throw. The least expensive card is the card that completes none of them. The discipline is to count your opponents' open sequences as carefully as your own.
When not to use the discard window
Do not use the discard window when you are close to declaring. The risk of throwing a card your opponent needs is worth the cost of throwing a card you might still use. The discard window is for the middle of the round, not the end.
