Sport a red frill (5)
I believe the answer is:
ruche
'frill' is the definition.
(I've seen this before)
'sport a red' is the wordplay.
'sport' becomes 'RU' (rugby union).
'a red' becomes 'che' (as in Che Guevara, a communist or 'red').
'ru'+'che'='RUCHE'
(Other definitions for ruche that I've seen before include "Frilled cloth as neck decoration" , "Pleated strip of material" , "fabric that's concertinaed" , "Fancy border" , "Fabric frill or pleat" .)