Roger, protected by criminal, arrives at low point (6)
I believe the answer is:
trough
'low point' is the definition.
'roger protected by criminal' is the wordplay.
'roger' becomes 'r' (abbreviation used in radio communications).
'protected by' indicates putting letters inside.
'criminal' becomes 'tough' (tough can mean a violent person).
'r' inserted inside 'tough' is 'TROUGH'.
'arrives at' acts as a link.
(Other definitions for trough that I've seen before include "Container for cattle-feed" , "Depression - container for food or water for animals" , "Container from which cattle or horses feed" , "Farm food container" , "Long narrow container used to feed animals" .)