Definition of knock in:
(v) :
(snooker, transitive) To pot (a ball)
(v) :
(snooker, transitive) To score (a break)
(n) :
(card games, archaic) The game of lanterloo.
(v) :
(obsolete, Oxford University slang) To enter college after hours—after half-past ten at night when the doors have been locked.