Haggard chap with singular description of horse without jockey (9)
I believe the answer is:
riderless
'description of horse without jockey' is the definition.
(jockeys are horse-riders)
'haggard chap with singular' is the wordplay.
'haggard' becomes 'rider' (novelist H Rider Haggard).
'chap' becomes 'Les' (man's name).
'with' is a charade indicator (letters next to each other).
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'rider'+'les'+'s'='RIDERLESS'
(Other definitions for riderless that I've seen before include "Some Grand National runners may become so" , "without one taking seat" , "like liberty horses" , "With no one in the saddle" , "Without addendum" .)