Definition
Short selling reverses the normal buy-low-sell-high trade: you sell high first, buy low later. The trader borrows shares from a broker (paying a borrow fee), sells them at the current price, and closes the position by buying shares back and returning them. Profit = sell price − buy back price − borrow costs. Risk is theoretically unlimited (a stock can rise infinitely) while profit is capped at 100% (a stock can only fall to zero). Short squeezes — when a heavily-shorted stock rises sharply, forcing shorts to buy back at losses, which pushes the price higher, forcing more buybacks — can produce catastrophic losses. The 2021 GameStop episode is a famous example. Short selling serves important market functions: price discovery, corporate governance signals, and hedge construction — but it's not for beginners.
Example
A trader borrows and sells 100 shares of XYZ at $50 ($5,000 received). If XYZ falls to $30, they buy back at $3,000 and return the shares — profit of $2,000 minus borrow fees. If XYZ rises to $80, buying back costs $8,000 — a loss of $3,000 plus fees.
Frequently Asked Questions
Is short selling legal?
Yes, in nearly all major markets. It's a regulated activity — brokers require margin accounts and short positions have specific reporting rules (e.g., SEC 13F short interest filings).
What is a short squeeze?
A rapid price rise in a heavily-shorted stock that forces shorts to buy back at losses. The buying itself pushes the price higher, cascading into more forced closures. GameStop in January 2021 rose from $17 to $483 in weeks.
How do I protect against short squeeze risk?
Position sizing (never short more than you can afford to lose), stop-losses (mandatory when shorting), avoiding names with unusually high short interest (>30% of float), and never shorting into strength.