Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of telecom and diversified-media company Cablevision Systems (NYSE: CVC) were getting a big thumbs-down from the market today, falling as much as 17% in intraday trading after COO Tom Rutledge abruptly resigned.

So what: Stocks often take a hit following the resignation of a CEO or CFO -- could Cablevision's COO really be that important? The short answer is "yes." Wall Street analyst Craig Moffett called Rutledge "the hands-down best executive in the cable business," while The Financial Times said he's "widely considered to be the company's most important executive." The resignation led to stock downgrades from Bank of America, Miller Tabak, and ISI Group.

Now what: It seems tough to put a good spin on this. Rutledge has been credited with navigating Cablevision through a tough competitive environment and helping the company spin off AMC Networks (Nasdaq: AMCX) and Madison Square Garden (Nasdaq: MSG). That loss could create a significant void in Cablevision's leadership.

In light of Rutledge's resignation, there was some speculation that the Dolan family may try to take the company private. For public-market shareholders, that could be a glimmer of good news, since the Dolans would most likely have to pay a premium to make that happen.

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