Fought back at first, trapped by the tangled reeds (8)
I believe the answer is:
resisted
'fought back' is the definition.
(resisting is a kind of fighting back)
'first trapped by the tangled reeds' is the wordplay.
'first' becomes 'ist'.
'trapped by' means one lot of letters goes inside another.
'the tangled' indicates an anagram.
'reeds' is an anagram of 'resed'.
'ist' going within 'resed' is 'RESISTED'.
'at' is the link.
(Other definitions for resisted that I've seen before include "Put up opposition from editress" , "Stood firm, held out" , "Is desert to be opposed?" , "Sees dirt (anag)" , "Struggled against" .)