Plucky in sport (4)
I believe the answer is:
game
I believe this clue is a double definition.
'plucky' is the first definition.
(both can mean enthusiastic or willing)
'sport' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for game that I've seen before include "Something to play or to chase" , "See 21" , "Animal hunted for food or sport" , "Eg, football match" , "venison, say" .)