I know what you're doing now that the match is over (3,4,2,2)
I believe the answer is:
the game is up
'i know what you're doing now' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'the match is over' is the wordplay.
'match' becomes 'game' (I've seen this before).
'over' becomes 'up' (e.g. if your time is up it is over).
'the'+'game'+'is'+'up'='THE GAME IS UP'
'that' is the link.
Can you help me to learn more?
(Other definitions for the game is up that I've seen before include "The scheme has failed, all is revealed" , "One's crime is revealed" , "The beaters have done their work" , "Springer's been active" , "Plan or crime is revealed or foiled" .)