Judge boxing final with it (6)
I believe the answer is:
trendy
'with it' is the definition.
(thesaurus)
'judge boxing final' is the wordplay.
'judge' becomes 'try' (trying is a kind of judging).
'boxing' indicates putting letters inside ('box' can mean contain, as in to put in a box).
'final' becomes 'end' ('end' can be a synonym of 'final').
'try' placed around 'end' is 'TRENDY'.
(Other definitions for trendy that I've seen before include "With-it" , "Less sensible; a dye plant" , "Up-to-date with the latest fad" , "Cool" , "Hot" .)