Packing in sport (6)
I believe the answer is:
boxing
I believe this clue is a double definition.
'packing' is the first definition.
('boxing' can be a synonym of 'packing')
'sport' is the second definition.
(boxing is a kind of sport)
'in' is the link.
(Other definitions for boxing that I've seen before include "Ring sport" , "Packer's job" , "Pugilist's sport" , "Fighting in a ring" , "handling rights, possibly?" .)