The power struggle over the futures of CBS, home to the most-watched television network in the country, and Viacom, which owns cable channels like MTV and Comedy Central, is marked by family politics, strong egos and relentless competitive pressure.

Shari Redstone, the president of National Amusements, which controls both companies, is in the thick of a public clash with Leslie Moonves, the chief executive of CBS, where Ms. Redstone is vice chairwoman.

She wants to combine CBS and Viacom. He is less enthused.

On Thursday, a Delaware judge handed Ms. Redstone a win. CBS was denied its request for a temporary restraining order that would have barred Ms. Redstone from having what is perceived as outsize influence over a board meeting Thursday evening where members took up a proposal to reduce her voting stake in CBS to about 20 percent from 79 percent.

Eleven board members voted in favor of the plan, and three voted against it. Ms. Redstone claimed victory, saying a bylaw change she had enacted required 90 percent of the board to approve. But the legal fight is far from over.