Jockeys (6)
I believe the answer is:
riders
'jockeys' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for riders that I've seen before include "they mount up" , "Jockeys" , "Travellers on bikes or horses" , "Clauses appended to a legislative bill" , "Clauses appended to legislative bills" .)