After the Department of Justice (DOJ) kicked off its argument that Alphabet (GOOG, GOOGL) holds an illegal monopoly over the online advertising market, Yahoo Finance legal reporter Alexis Keenan joined Julie Hyman and Josh Lipton on Market Domination to outline what happened the first day in court.

The antitrust case is "about online advertising, but if you ask the DOJ and you ask Google, 'What is this market?' they don't agree at all," Keenan said. The DOJ argued that the ad tech market comprises a group of niche markets. It called executives from publishing, advertising, and exchange companies as witnesses to bolster its claims that the ad tech market is made up of niche subsections.

On the other hand, Google says that all online advertising, including streaming, social media, and others, is one big market. This argument could allow Google to name Meta Platforms (META), Amazon (AMZN), and Microsoft (MSFT), among other big tech companies, as competitors in the space, making it easier to say there is competition within the space.

"It's going to be a tough argument for Google," Keenan said, noting that "the bottom line here is harm to consumers; that's what the judge cares about."

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This post was written by Naomi Buchanan.