Overwhelmed by fighting, I have to surrender (6)
I believe the answer is:
waiver
'surrender' is the definition.
(I've seen this before)
'overwhelmed by fighting i have' is the wordplay.
'overwhelmed by' is an insertion indicator (inserted letters get absorbed or overwhelmed).
'fighting' becomes 'war'.
'i have' becomes 'I've' (contraction of 'I have').
'war' placed around 'ive' is 'WAIVER'.
'to' is the link.
(Other definitions for waiver that I've seen before include "Disclaimer of a legal right" , "Formal for going of legal right or claim" , "withdrawal of claim" , "Formal written statement of relinquishment" , "Act of forgoing a right or claim" .)