Firing from big guns upset native (5)
I believe the answer is:
arson
'firing' is the definition.
(starting fires)
'big guns upset native' is the wordplay.
'big guns' becomes 'RA' (Royal Artillery).
'upset' shows that the letters should be reversed in order.
'native' becomes 'son' (a 'son' of a particular place is a native of it).
'ra' in reverse letter order is 'ar'.
'ar'+'son'='ARSON'
'from' acts as a link.
(Other definitions for arson that I've seen before include "A burning crime" , "Malicious crime" , "Be pettish" , "Roans (anag)" , "Crime of fire setting" .)