Being awfully rude on ship due to coercion (6)
I believe the answer is:
duress
'coercion' is the definition.
(under duress means being coerced)
'being awfully rude on ship' is the wordplay.
'being awfully' indicates anagramming the letters.
'on' says to put letters next to each other.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'rude' with letters rearranged gives 'dure'.
'dure'+'ss'='DURESS'
'due to' acts as a link.
(Other definitions for duress that I've seen before include "Restraint" , "Constraint, Compulsion" , "Threat of coercion" , "Pressure applied by druses" , "Threats, violence, etc, used in coercion" .)