Action shattered tablet (6)
I believe the answer is:
battle
'action' is the definition.
(military action)
'shattered tablet' is the wordplay.
'shattered' is an anagram indicator.
'tablet' is an anagram of 'BATTLE'.
(Other definitions for battle that I've seen before include "Sussex town" , "Military fight" , "Naval engagement" , "Military engagement" , "Lengthy fight" .)