Horn working for racing driver (6)
I believe the answer is:
button
'racing driver' is the definition.
(F1 driver Jenson Button)
'horn working' is the wordplay.
'horn' becomes 'butt' ((as an animal) to attack with the head or horns).
'working' becomes 'on'.
'butt'+'on'='BUTTON'
'for' acts as a link.
(Other definitions for button that I've seen before include "On-screen control" , "Push it or do it up!" , "Knob for fastening" , "Disc for pushing, fastening" , "Knob or disc as clothes fastener" .)