Running ahead, look back (6)
I believe the answer is:
upkeep
'running' is the definition.
(thesaurus)
'ahead look back' is the wordplay.
'ahead' becomes 'up' (similar in meaning).
'look' becomes 'peek' (peek can mean to look at quickly).
'back' shows that the letters should be reversed in order.
'peek' backwards is 'keep'.
'up'+'keep'='UPKEEP'
(Other definitions for upkeep that I've seen before include "Cost of support" , "Cost of maintaining" , "Running costs" , "Peek up at the maintenance" , "Looking after" .)