Release a French rugby player (6)
I believe the answer is:
unlock
'release' is the definition.
(I've seen this in another clue)
'a french rugby player' is the wordplay.
'a french' becomes 'un' ('a' in French).
'rugby player' becomes 'lock' (second row of a scrum).
'un'+'lock'='UNLOCK'
(Other definitions for unlock that I've seen before include "Crop" , "Open with key" , "Release bolt" , "Release with a key" .)