Career on the line? (7)
I believe the answer is:
calling
I believe this clue is a double definition.
'career' is the first definition.
('calling' can be a synonym of 'career')
'the line?' is the second definition.
(calling is a kind of line)
'on' is the link.
(Other definitions for calling that I've seen before include "Vocation or profession" , "Predicting the outcome" , "Ringing" , "visiting" , "Urge to follow a particular career" .)