Lock up criminal over financial penalty (7)
I believe the answer is:
confine
'lock' is the definition.
(thesaurus)
'up criminal over financial penalty' is the wordplay.
'up criminal' becomes 'con' (abbreviation for 'convict'. I am not sure about the 'up' bit.).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'financial penalty' becomes 'fine' (a payment extracted as punishment).
'con'+'fine'='CONFINE'
Can you help me to learn more?
(Other definitions for confine that I've seen before include "Shut in" , "Incarcerate" , "Keep within limits" , "Limit" , "Restrict (to an area)" .)