Working class making start (5)
I believe the answer is:
onset
'start' is the definition.
(onset is a kind of start)
'working class' is the wordplay.
'working' becomes 'on'.
'class' becomes 'set' (I've seen this before).
'on'+'set'='ONSET'
'making' acts as a link.
(Other definitions for onset that I've seen before include "Assault; beginning" , "Advent" , "Beginning (of disease etc)" , "Start - opening moments" , "Beginning; violent attack" .)