Back favourites for pace (4)
I believe the answer is:
step
'for pace' is the definition.
(synonyms)
'back favourites' is the wordplay.
'back' says the letters should be written backwards.
'favourites' becomes 'pets' ('pet' can be a synonym of 'favourite').
'pets' reversed gives 'STEP'.
(Other definitions for step that I've seen before include "Action of the leg" , "Tread - stage" , "Stage - pace" , "Pace; foothold" , "Manner of walking" .)