One fights egg producer with rowing team (12)
I believe the answer is:
bantamweight
'one fights' is the definition.
(bantamweight is a type of boxer)
'egg producer with rowing team' is the wordplay.
'egg producer' becomes 'bantam' (bantam is a type of chicken).
'with' becomes 'w' (abbreviation).
'rowing team' becomes 'eight' (eight rowers).
'bantam'+'w'+'eight'='BANTAMWEIGHT'
(Other definitions for bantamweight that I've seen before include "fighter" , "Boxing category" .)