Cribbage was a card game. In 1852, Ada Lovelace regularly played 5-card cribbage at the Papplewick Arms. She did so in secret, escaping from Newstead Abbey at night, as Colonel Wildman had been instructed not to allow her to engage in gambling.
The 5-card variation of cribbage required players to team up in pairs.
On the night after first meeting her, the Fourth Doctor found the pub which Lovelace frequented. Rather than outright oppose her interest, the Doctor joined in. He partnered with Lovelace, competing against two other pairs, consisting, in some order, of Harry, Ted, George, and Charlie. Harry dealt. At the start of the game, one player put down a King for 10, and the Doctor put down a Queen for 10. When another player put down an 8 for 18, the Doctor placed a 9, making 19, with Ada's approval.
Though he engaged with her interests, the Doctor questioned if gambling for farthings in a village pub was as noble a pursuit for Lovelace as were her unparalleled advancements in science. She claimed to see those two interests as entirely compatible, citing past endeavours to develop a mathematical model for placing large bets. After the game, Lovelace was happy to be "six shillings up", and proposed to play together with the Doctor again. (AUDIO: The Enchantress of Numbers)