Night SAS lost battle (8)
I believe the answer is:
hastings
'battle' is the definition.
(I know that Hastings is a pitched battle)
'night sas lost' is the wordplay.
'lost' is an anagram indicator.
'night'+'sas'='nightsas'
'nightsas' is an anagram of 'HASTINGS'.
(Other definitions for hastings that I've seen before include "His angst (anag.)" , "somewhere in Sussex" , "South coast resort" , "Ten Sixty-Six battle" , "Harold's objective?" .)