Another bout of selling gripped the U.S. stock market Friday, as anxiety mounts over whether the frenzy behind a swift, meteoric rise in GameStop and a handful of other stocks will damage Wall Street overall.

The S&P 500 dropped 1.9%, giving the benchmark index its biggest weekly loss since October. The Dow Jones Industrial Average and Nasdaq each fell 2%.

GameStop shot up nearly 70%, clawing back much of its steep loss from the day before, after Robinhood said it will allow customers to start buying some of the stock again. GameStop has been on a stupefying 1,600% run over the last three weeks and has become the battleground where swarms of smaller investors see themselves making an epic stand against the 1%.

The assault is directed squarely at hedge funds and other Wall Street titans that had bet the struggling video game retailer’s stock would fall. Those firms are taking sharp losses, and other investors say that’s pushing them to sell other stocks they own to raise cash. That, in turn, helps pull down parts of the market completely unrelated to the revolt underway by the cadre of smaller and novice investors.

The maniacal moves for GameStop and a few other formerly beaten-down stocks has drowned out many of the other issues weighing on markets, including the virus, vaccine rollouts and potential aid for the economy.

“Our consideration is whether this is something that is a long-term influence or contained within a handful of companies,” said Tom Hainlin, national investment strategist at U.S. Bank Wealth Management.

Meanwhile, calls for regulators to step in are growing louder on Capitol Hill, and the Securities and Exchange Commission says it’s carefully monitoring the situation.

“You’ve seen a lot of volatility this week, so when you have some unknowns like what you’re seeing in the retail trading world, people are a little concerned at record highs here and taking some money off the table,” said Megan Horneman, director of portfolio strategy at Verdence Capital Advisors.

The S&P 500 fell 73.14 points to 3,714.24. It ended the week with a 3.2% loss, its worst week in three months. It ended January with a 1.1% loss, its first monthly decline since October. The S&P 500 is still up 13.6% since the end of October.

Some of the heaviest weights on the index were Apple, Microsoft and other Big Tech stocks that have been big winners for professional and other investors during the last year.

The Dow lost 620.74 points to 29,982.62, while the tech-heavy Nasdaq composite slid 266.46 points to 13,070.69. The Russell 2000 index of smaller companies gave up 32.97 points, or 1.6%, to 2,073.64.

Other forces also weighed on the market. Johnson & Johnson fell 3.6% after it said its vaccine appears to protect against COVID-19, though not as powerfully as rivals. Analysts said the results, which would require just one shot instead of the two required by other vaccine makers, were below expectations.