Track on a hill (6)
I believe the answer is:
ascent
'hill' is the definition.
(I've seen this before)
'track on a' is the wordplay.
'track' becomes 'scent' (both can mean a trace left by someone).
'on' is a charade indicator (letters next to each other).
'scent' after 'a' is 'ASCENT'.
(Other definitions for ascent that I've seen before include "advancement" , "Enacts in climb" , "Upward slope" , "Act of moving upwards" , "Stance (anag)" .)