This is a big, big deal for Cablevision. Tom Rutledge is considered one of the best operators in the cable business — a level-headed guy and fierce competitor who’s equally comfortable handling questions about technology, finance, and marketing. Bernstein Research analyst Craig Moffett recently called Rutledge “arguably the most valuable executive in the cable industry.” That matters because investors also consider Rutledge to be a firewall protecting them from the craziness that always seems to surround Cablevision’s owners, the families of Charlies and Jim Dolan. The Dolans can’t afford to let investors wonder whether Cablevision’s going back to the days when it was paralyzed by family infighting and disastrous deals like the one Charles pushed to back the Voom collection of HD channels. Rutledge also is leaving just as some analysts wonder whether Cablevision’s best days are behind it: The stock price is down nearly 59% this year as video subscriptions have fallen. “Before 2011, Cablevision had historically posted revenue and EBITDA [cash flow] growth in-line or better than its publicly traded peers,” Moffett says. “Not anymore. Now, Cablevision looks like the sick man of the cable industry.”

Here’s the company’s statement:

BETHPAGE, NY– Cablevision Systems Corp. (NYSE: CVC) today announced that Tom Rutledge, chief operating officer, has informed the company that he will resign.

Mr. Rutledge joined Cablevision in 2002 as the company’s president of cable and communications. He became chief operating officer in 2004, assuming additional responsibilities for Cablevision’s Rainbow Media, which is now a separate public company called AMC Networks; Local Media properties including Newsday and other businesses and administrative functions.

“Everything I hoped for when I came to Cablevision has come true. I am proud of our record of success, and of the strong leadership team that remains in place to continue this work,” Mr. Rutledge said. “I have spent my entire working life – 34 years – in the cable industry, but my decade at Cablevision will always stand out because of the things we were able to achieve and the value we were able to deliver to customers in the most competitive market in the nation.”

James Dolan, Cablevision’s president and chief executive officer, commented: “Tom Rutledge has played a key role in driving and shaping Cablevision’s success over the last decade, applying a rare combination of technological vision and operational excellence that has delivered results. We are enormously thankful for his time here.”

Earlier this year, Mr. Rutledge was presented with the NCTA’s Distinguished Vanguard Award for Leadership, and was inducted into the Broadcasting & Cable Hall of Fame. He was inducted into the Cable Center Hall of Fame in 2009. His resignation will be effective later this month.

Cablevision indicated that it has an experienced senior management team in place overseeing cable and its other businesses, and that it has commenced a search for an executive with responsibility for oversight of the cable operations.