Where driver starts, about to steer over missile (6)
I believe the answer is:
exocet
'missile' is the definition.
(I've seen this before)
'where driver starts about to steer over' is the wordplay.
'where driver starts' becomes 'tee' (a golfer drives a ball from a tee).
'about' is an insertion indicator.
'to steer' becomes 'cox' (to cox is to steer a rowing boat).
'over' shows that the letters should be reversed in order.
'tee' going around 'cox' is 'tecoxe'.
'tecoxe' written backwards gives 'EXOCET'.
(Other definitions for exocet that I've seen before include "Subsonic, low-altitude missile" , "Short range guided missile" , "Weapon" , "Type of guided missile" , "Short-range guided missile" .)