Exploit that woman with Boat Race crew's pugilist (13)
I believe the answer is:
featherweight
'pugilist' is the definition.
(I know that featherweight is a type of pugilist)
'exploit that woman with boat race crew's' is the wordplay.
'exploit' becomes 'feat' (synonyms).
'that woman' becomes 'her' (her refers to a woman).
'with' becomes 'w' (abbreviation).
'boat race crew' becomes 'eight' (I've seen this before).
'feat'+'her'+'w'+'eight'='FEATHERWEIGHT'
(Other definitions for featherweight that I've seen before include "Light boxer" , "Light and of little importance" , "Boxer; person not worth serious consideration" , "one might be counted out?" , "Boxing category" .)