Casual worker following start of race (7)
I believe the answer is:
offhand
'casual' is the definition.
('offhand' can be a synonym of 'casual')
'worker following start of race' is the wordplay.
'worker' becomes 'hand' (hand is a kind of worker**).
'following' is a charade indicator (letters next to each other).
'start of race' becomes 'off'.
'hand' after 'off' is 'OFFHAND'.
(Other definitions for offhand that I've seen before include "Without thought" , "Casual; unconcerned" , "Cavalier" , "Dismissive; curt" , "Casual or curt, like discarded glove?" .)