How the mother of all ‘short squeezes’ helped drive stocks to historic gains Wednesday

A massive number of hedge fund short sellers rushed to close out their positions during Wednesday afternoon’s sudden surge in stocks, turning a stunning rally into one for the history books.

Traders — betting on share price declines — had piled on a record number of short bets against U.S. stocks ahead of Wednesday as President Donald Trump initially rolled out steeper-than-expected tariffs.

In order to sell short, hedge funds borrow the security they’re betting against from a bank and sell it. Then as the security decreases in price from where they sold it, they buy it back more cheaply and return it to the bank, profiting from the difference.

But sometimes that can backfire.

As stocks soared on news of the tariff pause, hedge funds were forced to buy back their borrowed stocks rapidly in order to limit their losses, a Wall Street phenomenon known as a short squeeze. With this artificial buying force pushing it higher, the S&P 500 ended up with its third-biggest gain since World War II.

Coming into Wednesday, short positioning was almost twice as much as the size seen in the first quarter of 2020 amid the onset of the Covid pandemic, according to Bank of America. As funds ran to cover, a basket of the most shorted stocks surged by 12.5% on Wednesday, according to Goldman Sachs, pulling off a larger jump than the S&P 500‘s 9.5% gain.

And a whopping 30 billion shares traded on U.S. exchanges during the session, marking the heaviest volume day on record, according to Nasdaq and FactSet data going back 18 years.

“You can’t catch a move. When you see someone short covering, the exit doors become so small because of these crowded trades,” said Jeff Kilburg, KKM Financial CEO and CIO. “We live in a world where there’s more and more twitchiness to the marketplace, there’s more and more paranoia.”

Of course, there were real buyers, too. Long-only funds bought a record amount of tech stocks during the session, especially the last three hours of the day, according to data from Bank of America.

But traders credit the shorts running for cover for the magnitude of the move.

“The pain on the short side is palpable; the whipsaw we have witnessed the past few weeks is extreme,” Oppenheimer’s trading desk said in a note. “What we saw in tech on that rise was obviously covering but more so real buyers adding on to higher quality semis.”

Thin liquidity also played a role in Wednesday’s monster moves. The size of stock futures (CME E-Mini S&P 500 Futures) one can trade with the click of your mouse dropped to an all-time low of $2 million on Monday, according to Goldman Sachs data. Drastically thin markets tends to fuel outsized price swings. 

Markets were pulling back Thursday as investors realized the economy is still in danger from super-high China tariffs and the uncertainty that daily negotiations with other countries will bring over the next three months.

There are still big short positions left in the market, traders said.

That could fuel things again, if the market starts to rally again.

“The desk view is that short covering is far from over,” Bank of America’s trading desk said in a note. “Our reasoning is that the market can’t de-risk a short in less than 3 hours which provided 20%+ SPX Index downside & major reduction in NET LEVERAGE over 7 seven weeks.”

“No shot it cleared in less than 3 hours,” Bank of America said.

Get Your Ticket to Pro LIVE

Join us at the New York Stock Exchange!Uncertain markets? Gain an edge with CNBC Pro LIVE, an exclusive, inaugural event at the historic New York Stock Exchange.

In today’s dynamic financial landscape, access to expert insights is paramount. As a CNBC Pro subscriber, we invite you to join us for our first exclusive, in-person CNBC Pro LIVE event at the iconic NYSE on Thursday, June 12.

Join interactive Pro clinics led by our Pros Carter Worth, Dan Niles and Dan Ives, with a special edition of Pro Talks with Tom Lee. You’ll also get the opportunity to network with CNBC experts, talent and other Pro subscribers during an exciting cocktail hour on the legendary trading floor. Tickets are limited!