Rider who's got the hump has brawl in coach (8)
I believe the answer is:
cameleer
'rider' is the definition.
(rider of a camel)
'brawl in coach' is the wordplay.
'brawl' becomes 'melee' (I've seen this before).
'in' is an insertion indicator.
'coach' becomes 'car' (as in a train coach or car).
'melee' going into 'car' is 'CAMELEER'.
'who's got the hump has' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for cameleer that I've seen before include "One driving across the Sahara" , "one in a caravan maybe" , "Desert traveller" , "Driver" , "Rider" .)