Reaction on press broadcast? Ecstasy! (8)
I believe the answer is:
response
'reaction' is the definition.
('response' can be a synonym of 'reaction')
'on press broadcast? ecstasy' is the wordplay.
'broadcast?' indicates an anagram (I've seen 'broadcast' mean this).
'ecstasy' becomes 'e' (informal term for the drug).
'on'+'press'='onpress'
'onpress' with letters rearranged gives 'respons'.
'respons'+'e'='RESPONSE'
(Other definitions for response that I've seen before include "comeback" , "'Answer, reply (8)'" , "Reply, rejoinder" , "Sees porn (anag) - answer" , "counter" .)