Pitched support for monarch on the radio (6)
I believe the answer is:
thrown
'pitched' is the definition.
'support for monarch on the radio' is the wordplay.
'support for monarch' becomes 'throne'.
'on the radio' indicates a 'sounds like' (homophone) clue.
'throne' sounds like 'THROWN'.
(Other definitions for thrown that I've seen before include "Tossed" , "Confused - cast" , "Confused; chucked" , "Parties are" , "Hurled, flung" .)