Displaying calm — no one was affected (5)
I believe the answer is:
posed
'was affected' is the definition.
(pose can mean to affect or pretend)
'displaying calm no one' is the wordplay.
'displaying calm' becomes 'poised' (poised means calm or composed).
'no' suggests deleting specific letters.
'one' becomes 'i' (Roman numeral).
'poised' with 'i' removed is 'POSED'.
(Other definitions for posed that I've seen before include "Assumed" , "Struck attitude, perhaps for painter" , "Modelled" , "Sat (for artist)" , "Took a stance" .)