One enforcing traveling rules (3)

I believe the answer is:

ref

(Other definitions for ref that I've seen before include "Middleman needing cards" , "Football's whistler" , "Sports official (abbrev.)" , "Whistleblower (abbr)" , "Football official (colloq.)" .)

I've seen this clue in The New York Times.

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.