Green’s Dictionary of Slang

an assistant or lookout man for a criminal gang or team of fraudsters.

1552

G. Walker Detection of Vyle and Detestable Use of Dice Play 29: This new-nurtured novice [...] is become so good a scholar, that he knoweth readily his flats and barris, and hath been snapper with the old cole at 2 or 3 deep strokes.