Try boxing contest carrying more weight (7)
I believe the answer is:
heavier
'carrying more weight' is the definition.
I can't tell whether this defines the answer.
'try boxing contest' is the wordplay.
'try' becomes 'hear' ('hear' can be a synonym of 'try').
'boxing' indicates putting letters inside ('box' can mean contain, as in to put in a box).
'contest' becomes 'vie' (I've seen this before).
'hear' enclosing 'vie' is 'HEAVIER'.
Can you help me to learn more?
(Other definitions for heavier that I've seen before include "More difficult to lift" , "Less light" , "more ponderous" , "Weightier" , "with 6D [SPARE TYRE] ?" .)