Current going round Circle Line track (6)
I believe the answer is:
follow
'track' is the definition.
(I've seen this in another clue)
'current going round circle line' is the wordplay.
'current' becomes 'flow' (synonyms).
'going round' indicates putting letters inside (some letters go around others).
'circle' becomes 'O' (O is a circle).
'line' becomes 'l' (used when specifying particular lines from a poem).
'o'+'l'='ol'
'flow' enclosing 'ol' is 'FOLLOW'.
(Other definitions for follow that I've seen before include "'____ and don't dilly-dally on the way'" , "dog" , "Grasp" , "Go along (a route)" , "Pursue or understand" .)