The troubled tycoons were guests on "NTVshniki," and the topic for the show, which was to air uncut late Sunday, was the global financial crisis.
In a short segment aired by NTV news on Saturday, Polonsky criticized the other guests on the panel while fielding questions from the audience, saying their comments put him "in a mind to punch someone's face."
Lebedev, sitting next to him, inquired whether the remark was directed at him. Polonsky asked him to calm down and continued his heated rant. Lebedev leapt out of his chair and dealt several blows to Polonsky's head, causing Polonsky to topple onto the floor together with his chair. The segment ends with the host calling for help from security guards.
Lebedev wrote on his blog Saturday that Polonsky was aggressive and "off his rocker" throughout the show and had to be "neutralized." He added that they had never met before.
Polonsky, 38, founder of the now-defunct Mirax Group and once ranked on Russia's billionaire list, saw his fortune decrease drastically after the 2008 recession. NTV estimated it at $200 million.
Lebedev, 51, controls the National Reserve Corporation and owns several newspapers, including Britain's The Independent and Evening Standard. The businessman, whose net worth was put at $2.1 billion by Forbes Russia this year, has complained in recent months that his companies face harassment from the Federal Security Service.