Green’s Dictionary of Slang

(UK Und.) a thug who works in a criminal gang and helps lure victims into a position where they might be robbed, with or without violence.

1614		Jonson Bartholomew Fair IV iii: One Val Cutting [...] a circling boy: with whom your Numps is so taken.
1822		R. Nares Gloss. (1888) I 163: A circling boy. A species of roarer; one who in some way drew a man into a snare, to cheat or rob him.