Laborious effort of a few inside track (7)
I believe the answer is:
travail
'laborious effort' is the definition.
(I've seen this before)
'a few inside track' is the wordplay.
'few' becomes 'v'.
'inside' indicates putting letters inside.
'track' becomes 'trail' ('trail' can be a synonym of 'track'**).
'a'+'v'='av'
'av' put inside 'trail' is 'TRAVAIL'.
'of' acts as a link.
(Other definitions for travail that I've seen before include "Hard labour" , "painful exercise" , "Toil - anguish" , "Painful or laborious effort, like childbirth" , "Labour, toil" .)