Line up outside initially under coercion (6)
I believe the answer is:
duress
'coercion' is the definition.
(thesaurus)
'line up outside initially under' is the wordplay.
'line up' becomes 'dress' ('dress' can be a synonym of 'line up').
'outside' means one lot of letters goes inside another.
'initially' suggests taking the first letters.
The initial letter of 'under' is 'u'.
'dress' going around 'u' is 'DURESS'.
(Other definitions for duress that I've seen before include "Use of force or threats to get something" , "The use of force or threats to get one's way" , "Hardship" , "Use of force or threats, often vile" , "Restraint" .)