Quiet performance mainly in movement, eerie initially (4)
I believe the answer is:
mime
'quiet performance' is the definition.
(a mime performs without speaking)
'mainly in movement eerie initially' is the wordplay.
'initially' says to take the initial letters.
The initial letters of 'mainly in movement eerie' is 'MIME'.
(Other definitions for mime that I've seen before include "Theatre with no speech" , "Acting without speaking" , "Charade" , "Silent performance" , "Silent play" .)