Veteran trader Art Cashin said that the market is experiencing a broad selloff, but the cause is not immediately clear.
Cashin, director of floor operations at the NYSE for UBS, told CNBC on Thursday that it is the riskier elements of the market that are being hit now, and he weighed whether this could be the start of something big.
"Rumor-mongers are out and about so the viewers should be careful," Cashin warned, adding that "it's clearly rather heavy selling ... there's nothing narrow about this selloff."
By noon on Thursday the Dow Jones industrial average had lost more than 200 points, the S&P 500 had dropped over 25 and the Nasdaq had fallen about 75. The Dow ended the day down 264 points, the S&P 500 shed 32 and Nasdaq slid 88 points.
As to what is causing markets' slide, Cashin dismissed the idea that the "sell on Rosh Hashana" theory is solely behind it.
"There are also speculations that some people have had to get into a position of liquidating," Cashin said, explaining that he has not been able to determine if this includes multiple parties, but either way "it's very broad selling."
On Thursday afternoon Cashin discussed the markets' current support levels, and what may be in store for the future.
"You've taken out the 50-day moving average rather handily in the S&P, so I would guess somewhere around 1,963 to 1,967. There's a band in there," he said. "If we get late-day selling and they go down through that, tomorrow could be a real problem. This might be setting up into one of those September-October things if that happens."
Last Friday Cashin had warned investors about this week: In his daily market notes he cited research showing Sept. 22 has been tied to market reversals, and he reported (with the acknowledgement it may be crazy) that "several of the astrological types claim their charts show next week is fertile ground for surprises."