Right on a line (5)
I believe the answer is:
legal
'right' is the definition.
(legal right is a kind of right)
'on a line' is the wordplay.
'on' becomes 'leg' (cricket term, fielding positions).
'line' becomes 'l' (used when specifying particular lines from a poem).
'leg'+'a'+'l'='LEGAL'
(Other definitions for legal that I've seen before include "Observing acts" , "Street - (1978 Dylan album)" , "Licit" , "Within bounds of law" , "In accordance with law" .)