Click this button to double your bet on this hand and take only one additional card. After drawing the additional card the hand is finished. This button is highlighted in the 1-deck game only when the non-split hand consists of two cards and has a value of 9, 10, or 11, and in the 6-deck game when the hand consists of any two cards, even after a split.
against a 6, there are several hands you'd want to double with