“We’ve never been as concerned as we are following this ruling,” said Ben Schachter, an analyst with Macquarie Securities, after the fine was announced.

The impact is hard to discern, because it’s impossible to judge whether Google has done wrong — and if so, how to make things right — without delving into minute detail about software algorithms and concepts like “consumer harm.” Explaining all that, in a way that ordinary people can understand, has been Yelp’s principal challenge with regulators. The war over how Google serves up information has been an information war.

The Yelp Flu

In summer 2004, a few months before the highly anticipated moment when Google first took its shares to market, Mr. Stoppelman got the flu. He searched the internet for a doctor, but instead of learning anything — like whether a doctor’s patients were satisfied, or the ease of getting an appointment — he kept landing on insurance websites.

This gave him an idea: How about a site where users rate and review local services? He and a co-founder got $1 million from investors and began work on the site that became Yelp. A year later, Yelp signed a two-year licensing deal that allowed Google to use Yelp content.

“It was better to be friends than enemies at that stage,” Mr. Stoppelman said.

Later, when the deal came up for renewal, Google told Mr. Stoppelman that it would soon add a feature allowing its own users to review and rate local services. Worried that Google wanted to create a parallel service that would snuff out his company, Mr. Stoppelman declined to renew the license.

Two years later, Google offered to buy Yelp for $550 million. One concern analysts raised about the proposed deal was that if Google owned Yelp, it might steer users toward Yelp instead of its organic search results — that is, the kind of steering Yelp says Google is now doing for its own benefit. The deal fell apart, however, and Google focused instead on building its own offering.

By 2011, Google was facing inquiries by various federal and state authorities along with regulators in Europe and Asia. It had steadily added services focused on areas like local businesses, comparison shopping and travel, and companies were complaining that it was giving its own properties preferred treatment in results.