Prominent boxer interrupting broadcast (7)
I believe the answer is:
salient
'prominent' is the definition.
(I know that prominent can be written as salient)
'boxer interrupting broadcast' is the wordplay.
'boxer' becomes 'Ali' (Muhammad Ali).
'interrupting' means one lot of letters goes inside another.
'broadcast' becomes 'sent' (sent or transmitted as a broadcast).
'ali' put within 'sent' is 'SALIENT'.
(Other definitions for salient that I've seen before include "Outstanding - it's lean (anag)" , "Foremost" , "part of defences" , "Prominent - in tales (anag)" , "Noteworthy" .)