Haggard motorcylist? (5)
I believe the answer is:
rider
'haggard' is the definition.
(novelist H Rider Haggard)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for rider that I've seen before include "Person on horseback" , "Equestrian - clause" , "Added proviso" , "Additional bit" , "Equestrian addition by a jury" .)