Glossary
Short squeeze
A rapid price rise driven by short sellers rushing to buy back borrowed shares, which feeds the very rally that is forcing them out.
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A short squeeze happens when a heavily shorted stock starts to rise and short sellers buy shares to close their positions, either to cap their losses or because a broker forces them to. Those purchases push the price higher still, which pressures the next group of shorts, and the loop can drive a stock up far faster than news alone would.
How it unfolds
Squeezes need fuel and a spark. The fuel is a crowded short: high short interest relative to the float, and many days to cover. The spark is anything that lifts the price: a strong earnings report, a buyout rumor, or a wave of coordinated buying. Rising borrow fees and margin calls then turn voluntary covering into forced buying.
GameStop in January 2021 is the best-known case. Short interest had been above 100% of its float, and the share price went from under $20 at the end of 2020 to an intraday peak above $480 on January 28 (prices before the 2022 four-for-one split), then fell back sharply. The SEC staff report on those weeks found that short covering was only a small share of the buying; investors opening new long positions drove most of it.
What to watch for
Squeezes end abruptly, and the reversal can be as violent as the rise. Late buyers often pay the highest prices, and trading halts and wide spreads are common at the peak. High short interest alone predicts nothing: many crowded shorts simply keep falling.