Ran opinion piece supporting hostility (8)
I believe the answer is:
galloped
'ran' is the definition.
(gallop can mean to run fast)
'opinion piece supporting hostility' is the wordplay.
'opinion piece' becomes 'op-ed' (part of a newspaper offering opinion pieces).
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'hostility' becomes 'gall' (gall is a kind of hostility).
'oped' put after 'gall' is 'GALLOPED'.
(Other definitions for galloped that I've seen before include "Went at a very fast gait" , "what did Joris and Dirck do?" , "Went quickly by horse" , "Rode fast" , "Moved fast like a horse" .)