Goad retreating rugby players heartlessly (4)
I believe the answer is:
spur
'goad' is the definition.
(spur is a kind of goad)
'retreating rugby players heartlessly' is the wordplay.
'retreating' shows that the letters should be reversed in order.
'rugby' becomes 'ru'.
'heartlessly' says to hollow out the word (remove centre letters).
'players' with its middle removed is 'ps'.
'ru'+'ps'='rups'
'rups' written backwards gives 'SPUR'.
(Other definitions for spur that I've seen before include "Incite to action" , "Goad as for a horse" , "Goad, prod" , "Cowboy boot attachment" , "Impel" .)