Perhaps a setter to follow? (3)
I believe the answer is:
dog
'to follow?' is the definition.
(dog can mean to follow or torment)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for dog that I've seen before include "A pet; its life prov. wretched" , "'Every ... is allowed one bite'" , "plague?" , "'You cannot teach an old ... new tricks'" , "Follow - canine" .)