Fiery editor sat on by police in America (6)
I believe the answer is:
heated
'fiery' is the definition.
(heated up with fire)
'editor sat on by police in america' is the wordplay.
'editor' becomes 'ed'.
'sat on by' means one lot of letters go next to another.
'police in america' becomes 'heat' (informal US term for the police).
'ed' put after 'heat' is 'HEATED'.
(Other definitions for heated that I've seen before include "Angry, getting warm" , "Baked; angry" , "Fired-up" , "Angry - passionate" , "Of discussion, angry and hostile" .)