Work hard for a victory in track (7)
I believe the answer is:
travail
'work hard' is the definition.
(I've seen this before)
'a victory in track' is the wordplay.
'victory' becomes 'v'.
'in' indicates putting letters inside.
'track' becomes 'trail' ('trail' can be a synonym of 'track'**).
'a'+'v'='av'
'av' put within 'trail' is 'TRAVAIL'.
'for' acts as a link.
(Other definitions for travail that I've seen before include "In old use, the pains of childbirth" , "Use of physical or mental energy; excessive labour..." , "Hard work" , "Painful or laborious effort, like childbirth" , "Toil - anguish" .)