Champion rugby player working at hospital department (9)
I believe the answer is:
proponent
'champion' is the definition.
(both can mean an endorser or supporter)
'rugby player working at hospital department' is the wordplay.
'rugby player' becomes 'prop' (I've seen this before).
'working' becomes 'on' (on can mean working or activated).
'at' means one lot of letters go next to another.
'hospital department' becomes 'ENT' (abbreviation for Ear, Nose and Throat department).
'prop'+'on'+'ent'='PROPONENT'
(Another definition for proponent that I've seen is " Advocate (of a theory, etc)".)