The knight must have a win, on the other hand (4,5)
I believe the answer is:
then again
'on the other hand' is the definition.
(synonyms)
'the knight must have a win' is the wordplay.
'knight' becomes 'n' (chess abbreviation).
'must have' is a charade indicator (letters next to each other).
'win' becomes 'gain' (synonyms).
'the'+'n'+'a'+'gain'='THEN AGAIN'
(Other definitions for then again that I've seen before include "From another point of view" , "however" , "still" .)