Scoundrels are hard on Parramatta players (5)
I believe the answer is:
heels
'scoundrels' is the definition.
(heel is a kind of scoundrel)
'hard on parramatta players' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'parramatta players' becomes 'Eels' (rugby team Parramatta Eels).
'h'+'eels'='HEELS'
'are' acts as a link.
(Other definitions for heels that I've seen before include "Cobbler does this" , "Blackguards in shoes?" , "leans to one side" , "Cads - shoe parts" , "Wedges" .)