A sport's meaning for defender (9)
I believe the answer is:
apologist
'defender' is the definition.
(thesaurus)
'a sport's meaning' is the wordplay.
'sport' becomes 'polo' (polo is a kind of sport**).
'meaning' becomes 'gist' (gist is a kind of meaning).
'a'+'polo'+'gist'='APOLOGIST'
'for' is the link.
(Other definitions for apologist that I've seen before include "Advocate" , "Person who argues to defend or justify some policy" , "Justifier" , "Champion" , "One who argues in favour of something controversial" .)