Surprise shots at men in a melee (12)
I believe the answer is:
astonishment
'surprise' is the definition.
(thesaurus)
'shots at men in a melee' is the wordplay.
'a melee' indicates anagramming the letters.
'shots'+'at'+'men'+'in'='shotsatmenin'
'shotsatmenin' anagrammed gives 'ASTONISHMENT'.
(Other definitions for astonishment that I've seen before include "Amazement" , "Great surprise" , "Cause of dumbness" , "Stupefaction" , "Wonder" .)