A name given to the person who with a whip in his hand, and a hat held before his eye, keeps the ring clear, at boxing-matches and cudgel-playing; also, in cant terms, a cloak.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
See also the definition in Nathan Bailey's 1736 dictionary of canting and thieving slang.
Vincent’s Law * VixenNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes