Inform of a competition reward on the radio (7)
I believe the answer is:
apprise
'inform of' is the definition.
(I've seen this before)
'a competition reward on the radio' is the wordplay.
'a competition' becomes 'ap' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'reward' becomes 'prize' (I've seen this before).
'on the radio' indicates a 'sounds like' (homophone) clue.
'prize' is a homophone of 'prise'.
'ap'+'prise'='APPRISE'
Can you help me to learn more?
(Other definitions for apprise that I've seen before include "Formally inform, notify" , "Provide with information" , "Inform, make aware of" , "tip off" , "Inform, make known to" .)