Rugby player's retreat (4)
I believe the answer is:
back
This clue is a double definition.
'rugby player's' is the first definition.
'retreat' is the second definition.
(thesaurus)
(Other definitions for back that I've seen before include "player in line of defence?" , "Fashionable again" , "Series of popular time-travel movies" , "Support; in return" , "ago" .)