Blocked From the Bottom

A suit is blocked from the bottom when it is impossible for taker to lead each card in that suit and have giver follow suit with a smaller card. Having a two in a suit automatically blocks that suit from the bottom. Having two cards four or below blocks a suit from the bottom. So does three cards six or below, four cards eight or below, five cards ten or below, or six cards queen or below.

The significance of having a suit blocked from the bottom is that taker can never play all of his cards in the suit while giver still has cards left. If taker leads the suit long enough, either giver will run out or taker will have the lowest remaining card in the suit.

When the non-dealer looks at his hand and sees that all four suits are blocked from the bottom then he knows that it is mathematically impossible for him to make the hand.. His reasoning goes as follows:

To make this hand the team must take all tricks including the tenth trick. Take a close look at the suit of the giver's play to the last trick. Let's say that it was a heart. Taker's last card must also be a heart because if it wasn't then taker would already have played all of his cards in hearts while giver still had a heart left. However, the taker's remaining heart must be lower than the giver's lone card, otherwise this would also violate the fundamental rule of blocked suits; that the taker cannot play all of his cards in a suit as long as the giver has any left.