Cablevision has a new(ish) big stakeholder and things could get interesting as it is activist investor Harbinger Capital. According to a regulatory filing Harbinger now owns a combined 11 million shares in Cablevision through two funds as of June 30th, making it the 5th largest external stakeholder in the New York cable operator.

Harbinger, lest we forget, has been shoving around the media companies in which it has snapped up stakes to find to boost share prices, notably with New York Times and Media General earlier this year.

Harbinger will be joining Mario Gabelli (pictured left), of Gabelli & Co, which owns around 20 million Cablevision shares and has been very loudly pushing for the company to consider selling assets such as its cable networks. Gabelli wants Cablevision to use the funds from such an asset sale to buy back stock. Other big name Cablevision shareholders are ClearBridge Advisors (part of Legg Mason), T Rowe Price and London-based Marathon Asset Management.

Richard Greenfield of Pali Research, who brought the Harbinger filing to our attention, makes an interesting point that the top five stake holders now own 108 million of the total 295 million float. The Dolan family, who control the company, own around 72 million.

In Greenfield’s view:

This fact will help propel Cablevision shares if they begin to buy back shares in the fall.