Attack a sailor on the radio (7)
I believe the answer is:
assault
'attack' is the definition.
(I know that attack can be written as assault)
'a sailor on the radio' is the wordplay.
'sailor' becomes 'salt' (salt is a kind of sailor).
'on the radio' indicates a 'sounds like' (homophone) clue.
'salt' sounds like 'ssault'.
'a'+'ssault'='ASSAULT'
(Other definitions for assault that I've seen before include "Physical attack" , "Attack physically" , "Strike" , "Attack suddenly" , "The fool starts the attack" .)