New York squad turning up to make arrest (4)
I believe the answer is:
stem
'arrest' is the definition.
(both can mean to stop)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for stem that I've seen before include "part of a ship" , "Staunch - stalk" , "Stop the flow of, check" , "Stop or slow the flow of" , "Dam" .)