Editorial Note: OED has a sense of ringman ‘a sporting man; a bookmaker’ to which this could be related via an original shared meaning of ‘a person who occupies or attends an enclosed area.’
Citations:
1952 Aubrey graves @ Winchester, Va. Washington Post (Oct. 12) “Biggest Sale In East Held At Winchester” p. M17: The “ringman” in the foreground is Hugh Henderson. 1983 Robert Sheppard Globe and Mail (Toronto, Can.) (Oct. 29) “Western cattle make star trek to help bridge regional gap” p. P14: By a direct phone link, the Ontario buyers will be able to place bids with the ringman, who will pass them on to the auctioneer. 2005 Kerry Hall Charlotte Observer (N.C.) (July 27) “More real estate selling at auctions”: Within seconds, the bidding jumped from the asking price of $3.5 million to $4 million. Greene’s four assistants, or “ringmen” as they’re called, circulated the room, keeping track of the bids.