US arresting officer? (7)

I believe the answer is:

sheriff

(Other definitions for sheriff that I've seen before include "County official" , "Chief officer of the Crown in a county" , "Head of the posse" , "US law enforcement officer" , "Scots judge" .)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.