First, "there were reports in the media [saying] that the ECB and/or banking authorities suggested to banks to get rid of any sovereign Greek debt they had, which suggests that maybe the next step will be Greece exiting," Cashin told CNBC.
The second factor for the selloff is tied to Chinese authorities banning margin trades on over-the-counter stocks, Cashin added. "That whacked the after-hours futures by more than 5 percent."
Finally, the third factor driving the selloff is the temporary outage of the Bloomberg Terminal, which "was disruptive enough to force the U.K. to postpone a bond offering," Cashin also said.
Read MoreWhat is the Bloomberg Terminal?
These three factors have "taken the S&P 500 below what was pretty important support at 2,082 to 2,085. That is going to damage the chart and you run the risk, if they close below there, of setting up a negative chart," he said.
U.S. stocks were down more than 1 percent across the board, with the Dow Jones industrial average shedding about 285 points. Click here to see what the markets are doing now.