Finish off attack, sacrificing bishop (3,2)
I believe the answer is:
eat up
'finish off' is the definition.
(I've seen this in another clue)
'attack sacrificing bishop' is the wordplay.
'attack' becomes 'beat up' (to beat up is to attack violently).
'sacrificing' is a deletion indicator.
'bishop' becomes 'B' (abbreviation for bishop in chess).
'beatup' with 'b' taken away is 'EAT UP'.
(Other definitions for eat up that I've seen before include "finish meal" , "Devour entirely" , "Finish one's food" , "Consume, absorb" , "show good appetite" .)