BATS President William O’Brien quits exchange operator E-mail Tweet Facebook Google Plus Linkedin Share icons by Tom Huddleston, Jr. @FortuneMagazine July 22, 2014, 1:05 PM EDT BATS Global Markets, one of the country’s largest stock exchanges, said Tuesday that its president, William O’Brien, is stepping out of that role, effective immediately. In a press release, BATS gave no reason for O’Brien’s departure, which results in CEO Joe Ratterman reassuming the dual President-CEO title at the Lenexa, Kansas-based exchange. Ratterman previously held both titles until the BATS board decided to split the roles two years ago following the exchange’s withdrawal of its initial public offering due to a trading glitch. O’Brien assumed the role of president roughly six months ago after previously serving as CEO of New Jersey exchange Direct Edge, which merged with BATS earlier this year. In April, O’Brien made headlines when he appeared on CNBC and engaged in a heated argument with Flash Boys author Michael Lewis and IEX co-founder Brad Katsuyama, who is the focus of Lewis’ best-selling book and an outspoken opponent of high-frequency trading. The debate, which centered on how Direct Edge priced its trades, resulted in BATS issuing a correction of statements made by O’Brien during the interview in which he claimed the exchange did not use slower feeds for pricing. BATS said the rest of its executive team will remain unchanged.