Secure rugby player (4)
I believe the answer is:
lock
I believe this clue is a double definition.
'secure' is the first definition.
(locking is a kind of securing)
'rugby player' is the second definition.
(position in rugby)
(Other definitions for lock that I've seen before include "Hold < wisp of wool" , "Security device - tuft of hair" , "temporary container for lighter, say" , "Secure a piece of hair" , "Become immoveable" .)