Display garment for sportsperson (10)
I believe the answer is:
showjumper
'for sportsperson' is the definition.
(I've seen this before)
'display garment' is the wordplay.
'display' becomes 'show' (synonyms).
'garment' becomes 'jumper' (jumper is a kind of garment).
'show'+'jumper'='SHOWJUMPER'
(Other definitions for showjumper that I've seen before include "performer in event" , "equestrian" , "Sportsperson penalised for a refusal" , "one tackling obstacles in due course" , "one using mount?" .)