Brokers held the deck of customer orders and worked them in the pit, earning a fee per contract. The separation from locals mattered: rules against trading ahead of customer orders existed precisely because a broker knew what was coming.
Enforcement was imperfect, and the FBI's 1989 undercover investigation of the Chicago pits led to dozens of indictments and to reforms in audit trails and timestamping that shaped modern surveillance.
Example: a broker holding a 500-lot order to buy on the close had information nobody else had, which is why "trading ahead" became one of the first offences exchanges wrote rules against.
Related: pit-trading, locals, open-outcry, market-manipulation