Males losing head are contributors to rows (4)
I believe the answer is:
oars
'contributors to rows' is the definition.
(oars are used when rowing)
'males losing head' is the wordplay.
'males' becomes 'boars' (male pigs).
'losing head' means to remove the first letter.
'boars' with its first letter removed is 'OARS'.
'are' acts as a link.
(Other definitions for oars that I've seen before include "Implements to propel or steer on water" , "Boating implements" , "Means of propulsion" , "Propelling implements" , "Soar with propellors" .)