Amphitheatre gripped by warfare, naturally (5)
I believe the answer is:
arena
'amphitheatre' is the definition.
(I've seen this before)
'gripped by warfare naturally' is the wordplay.
'gripped by' indicates a hidden word.
'ARENA' is hidden within 'warfare naturally'.
(Other definitions for arena that I've seen before include "Wembley, say" , "Place for public contests" , "Stadium - battlefield" , "Where one may find sportsmen" , "Area in centre of sports stadium" .)