Loss of power consuming leader in Rome, a shocker (7)
I believe the answer is:
outrage
'a shocker' is the definition.
'loss of power consuming leader in rome' is the wordplay.
'loss of power' becomes 'outage' (I've seen this in another clue).
'consuming' indicates putting letters inside.
'leader in' says to take the initial letters.
The initial letter of 'rome' is 'r'.
'outage' placed around 'r' is 'OUTRAGE'.
(Other definitions for outrage that I've seen before include "furious reaction" , "Intolerable or shocking act, to argue about" , "Gross affront to decency" , "Appalled reaction" , "Shocking event" .)