Stop row about Greek character (6)
I believe the answer is:
detain
'stop' is the definition.
(I've seen this before)
'row about greek character' is the wordplay.
'row' becomes 'din' (both can mean a loud disturbance).
'about' means one lot of letters goes inside another.
'greek character' becomes 'eta' (letter from the Greek alphabet).
'din' enclosing 'eta' is 'DETAIN'.
(Other definitions for detain that I've seen before include "Hang on to" , "Keep in custody; hold back" , "Imprison" , "Confine" , "Sing to (someone)" .)