Slog in chase to secure a victory (7)
I believe the answer is:
travail
'slog' is the definition.
(thesaurus)
'chase to secure a victory' is the wordplay.
'chase' becomes 'trail' (synonyms).
'to secure' indicates putting letters inside.
'victory' becomes 'v'.
'a'+'v'='av'
'trail' going around 'av' is 'TRAVAIL'.
'in' is the link.
(Other definitions for travail that I've seen before include "Painful or laborious effort, like childbirth" , "Labour, toil" , "Hard work" , "Use of physical or mental energy; excessive labour..." , "In old use, the pains of childbirth" .)