Low volatility has been the norm in the market lately, and veteran trader Art Cashin thinks one reason may be that some high-frequency traders are sitting things out for the moment.
"With these investigations happening, some of the high-frequency traders may have decided that discretion is the better part of valor, and they're not playing," he told CNBC's "Closing Bell."
The latest accusations focus on Barclays. The New York State Attorney General alleges the firm used its private trading system, or dark pool, to benefit high-speed traders.
Securities and Exchange Commission Chair Mary Jo White has pledged to change high-frequency trading rules later this year.
However, high-speed traders aren't the only ones potentially sitting on the sidelines, Cashin said. Investors who did OK the first half of the year may have decided to rotate out of equities and into something with yield.
"I'm not sure all of the players are on the field, so that may be distorting things slightly," he said.
Just because there is low volatility now, Cashin said that doesn't necessary mean that bad times are ahead.
"You will hear a good deal of people saying that this much calm and complacence in the market will spring out in a negative fashion. That's certainly been true in some of the recent past, but there were stretches back in through the '50s and '60s where you had relative calm in the market followed by a rather better market. So I don't think that the record is clear enough that we can extrapolate from it."
—By CNBC's Michelle Fox