Struggle across line to finish (8)
I believe the answer is:
complete
'finish' is the definition.
('complete' can be a synonym of 'finish')
'struggle across line' is the wordplay.
'struggle' becomes 'compete' (I've seen this before).
'across' is an insertion indicator.
'line' becomes 'l'.
'compete' placed around 'l' is 'COMPLETE'.
'to' acts as a link.
(Other definitions for complete that I've seen before include "Intact" , "Execute" , "Finish; whole" , "Having all the necessary parts" , "Full" .)