A ship worker admits trouble from attacker (9)
I believe the answer is:
assailant
'attacker' is the definition.
('assailant' can be a synonym of 'attacker')
'a ship worker admits trouble' is the wordplay.
'ship' becomes 'ss'.
'worker' becomes 'ant' (worker is a type of ant).
'admits' indicates putting letters inside.
'trouble' becomes 'ail' ('ail' can be a synonym of 'trouble'**).
'ss'+'ant'='ssant'
'ssant' enclosing 'ail' is 'ssailant'.
'a'+'ssailant'='ASSAILANT'
'from' is the link.
(Other definitions for assailant that I've seen before include "who is on the offensive?" , "One attacking another" , "Aggressor" , "An attacker like mugger" , "Attacking person" .)