Person misusing horse? Put on an extra court (6)
I believe the answer is:
addict
'person' is the definition.
(addict is a kind of person)
'put on an extra court' is the wordplay.
'put on' becomes 'add' (as in adding something on).
'an' becomes 'i' (Roman numeral for one).
'extra court' becomes 'ct' (abbreviation used in road names. I am not sure about the 'extra' bit.).
'add'+'i'+'ct'='ADDICT'
'misusing horse?' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for addict that I've seen before include "Fanatic devotee" , "Enthusiast" , "One unable to kick habit" , "Habitual drug user" , "One dependent on drugs" .)