Elderly to harass racer (9)
I believe the answer is:
greyhound
'racer' is the definition.
(I know that greyhound is a type of racer)
'elderly to harass' is the wordplay.
'elderly' becomes 'grey' (I've seen this in other clues).
'to harass' becomes 'hound' (I've seen this in another clue).
'grey'+'hound'='GREYHOUND'
(Other definitions for greyhound that I've seen before include "Tall, slender canine" , "racer" , "Swift breed of dog" , "Dog trained for racing on tracks" , "Fast-moving dog" .)