Arrest Greek character involved in racket (6)
I believe the answer is:
detain
'arrest' is the definition.
(detain can mean to arrest or hold)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for detain that I've seen before include "Keep (someone) held in custody" , "Stop" , "Keep in custody or delay" , "Ate din (anag.)" , "Keep in official custody" .)