A sailor heard being offensive (7)
I believe the answer is:
assault
'being offensive' is the definition.
('assault' can be similar in meaning to 'offensive')
'a sailor heard' is the wordplay.
'sailor' becomes 'salt' (salt is a kind of sailor).
'heard' shows a homophone (sound like).
'salt' is a homophone of 'ssault'.
'a'+'ssault'='ASSAULT'
(Other definitions for assault that I've seen before include "offensive" , "Strike" , "The fool starts the attack" , "Attack physically" , "Mount an attack" .)