Shares of Comcast dove as much as 7 percent Thursday after one of its executives said the company expects a large subscriber loss during the third quarter. Comcast closed the day down 6.24 percent.

It was the biggest dive since Aug. 8, 2011, before the stock price regained some of the loss. By mid-afternoon, it was down 4.86 percent.

Matthew Strauss, executive vice president for Comcast's Xfinity services, said during a Merrill Lynch media conference that the company expects to report a loss of 100,000 to 150,000 subscribers during the third quarter.

Strauss blamed competition and Hurricane Harvey for the losses and said it's the "most competitive quarter" in recent history. Comcast, CNBC's parent company, is still expected to hit its other numbers.

Telsey Advisory Group senior research analyst Thomas Eagan thinks investors don't have that much to worry about. "The market has overreacted here. It seems more emotional than anything else," Eagen said. "We don't quite know much about the decline that the company mentioned today, how much of it is because of the hurricane and how much of it is because of competition."

Comcast and other traditional cable companies have had to fight to keep customers as lower price streaming TV services become more popular.

Disclosure: Comcast is the owner of NBCUniversal, the parent company of CNBC and CNBC.com.