Arrest Greek character involved in row (6)
I believe the answer is:
detain
'arrest' is the definition.
(I've seen this before)
'greek character involved in row' is the wordplay.
'greek character' becomes 'eta' (letter from the Greek alphabet).
'involved in' is an insertion indicator.
'row' becomes 'din' (both can mean a loud disturbance).
'eta' going within 'din' is 'DETAIN'.
(Other definitions for detain that I've seen before include "Hold back or keep under restraint" , "Hold back - arrest" , "put in jail" , "Delay, arrest" , "Ate din (anag.)" .)