Waving hats, sign for battle (8)
I believe the answer is:
hastings
'for battle' is the definition.
(Battle of Hastings, 1066 battle)
'waving hats sign' is the wordplay.
'waving' indicates an anagram (letters wave around).
'hats'+'sign'='hatssign'
'hatssign' anagrammed gives 'HASTINGS'.
(Other definitions for hastings that I've seen before include "Harold's objective?" , "English town" , "Ten sixty six battle" , "Sussex battle" , "Town in East Sussex" .)