Fight in Sussex town (6)
I believe the answer is:
battle
I believe this clue is a double definition.
'fight' is the first definition.
(I know that fight can be written as battle)
'sussex town' is the second definition.
(I've seen this before)
'in' acts as a link.
(Other definitions for battle that I've seen before include "Lengthy conflict" , "Lengthy fight" , "A fight between large forces" , "war" , "Sussex town" .)