The merit of rotgut, oddly, in struggle (6)
I believe the answer is:
virtue
'the merit' is the definition.
('virtue' can be a synonym of 'merit')
'rotgut oddly in struggle' is the wordplay.
'oddly' means one should take alternating letters.
'in' indicates putting letters inside.
'struggle' becomes 'vie' (I've seen this before).
The alternating letters of 'rotgut' are 'rtu'.
'rtu' inserted into 'vie' is 'VIRTUE'.
'of' acts as a link.
(Other definitions for virtue that I've seen before include "''....is it's own reward'' (6)" , "It's said to be its own reward" , "Admirable feature" , "Maybe hope" , "Moral excellence" .)