It was the fight that stopped trading on the floor of the New York Stock Exchange—IEX's Brad Katsuyama vs. BATS Global Markets president William O'Brien on high-speed trading and 'rigged' markets.

"You want to do this? Let's do this," Katsuyama said in response to O'Brien's prodding.



"I really do," O'Brien said.

(To watch the full 23 minutes of Katsuyama and Lewis vs. O'Brien, click here).

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And off they went, for more than 20 minutes. Traders stood transfixed as the two argued over the very nature of the stock market and whether the average investor could even compete with the big guys. (Twitter stopped too; see the tweets here).

(Watch: Michael Lewis on HFT)