Arrest Greek Character during row (6)
I believe the answer is:
detain
'arrest' is the definition.
(I've seen this before)
'greek character during row' is the wordplay.
'greek character' becomes 'eta' (letter from the Greek alphabet).
'during' means one lot of letters goes inside another.
'row' becomes 'din' (both can mean a loud disturbance).
'eta' inserted within 'din' is 'DETAIN'.
(Other definitions for detain that I've seen before include "Sing to (someone)" , "Hold back or keep under restraint" , "Ate din (anag.)" , "Keep in custody or delay" , "Hang on to" .)