In favour of not running quickly (6)
I believe the answer is:
pronto
'quickly' is the definition.
(I've seen this before)
'in favour of not running' is the wordplay.
'in favour of' becomes 'pro' (being pro a particular cause).
'running' is an anagram indicator (the letters run around to different places).
'not' with letters rearranged gives 'nto'.
'pro'+'nto'='PRONTO'
(Other definitions for pronto that I've seen before include "Double quick!" , "Right now, immediately" , "Quickly, amigo" , "Promptly, without delay" , "Right now, amigo" .)