Right on a length (5)
I believe the answer is:
legal
'right' is the definition.
(legal right is a kind of right)
'on a length' is the wordplay.
'on' becomes 'leg' (cricket term, fielding positions).
'length' becomes 'l'.
'leg'+'a'+'l'='LEGAL'
(Other definitions for legal that I've seen before include "Compliant with the law" , "associated with silk business?" , "Within bounds of law" , "Sound" , "It's acceptable" .)