What: Shares of video game maker Activision Blizzard (ATVI) dropped 10% in January according to S&P Capital IQ data, partially due to a share sale by one of its biggest shareholders.

So what: Mid-month, Vivendi SA, who acquired a 52% stake in Activision Blizzard in 2008, sold its remaining 5.7% stake in the business to unidentified financial institutions for $1.1 billion. This ends a long relationship between the companies. It has to concern investors that a big shareholder is selling right now. 

Activision Blizzard also announced the acquisition of Major League Gaming for $46 million. The acquisition is part of a plan to create the "ESPN of esports". 

Now what: I wouldn't worry too much about Vivendi selling shares -- the company has been shuffling assets to expand in pay TV and music. The Activision Blizzard sale will help fund some of that strategy.

Buying Major League Gaming could give the company insights into the habits and preferences of some of its more diehard customers.

All in all, I would chalk up the loss in January to market moves, but investors should pay attention to earnings, which will be out February 11 and will tell us how successful the video game business was during the holidays.