Why GameStop (GME) Has Gone Up So Much

GameStop's stock has gone from around $20 at the start of January 2021 to over $400 at this week's peak. That's a 20x move in three weeks, on a brick-and-mortar video game retailer with declining same-store sales. The explanations in the press range from "Reddit traders bullied a hedge fund" to "the markets are broken," and both are partly right but neither is the actual mechanic. The mechanic is two compounding squeezes (short and gamma) layered on a stock that the institutional shorts had over-bet against. Worth pulling apart, because this is the cleanest live example of how those squeezes work that most retail investors will see in their lifetime.

The Short Side: Over 100% Short Interest

Short selling is when you borrow a stock from someone who owns it, sell it on the market, and hope the price drops so you can buy it back cheaper, return it to the lender, and pocket the difference. The technical maximum for short interest in a stock is 100% of the float (the number of shares available to trade). Above that, you have shares being borrowed, sold to a new owner, then borrowed again from that new owner and sold a second time. It's legal, it's been a feature of US markets for decades, and it's also a structural risk most institutional shorts don't take seriously.

GameStop's short interest as of December 2020 was reportedly above 140% of float. That meant for every share that was actually owned by a long-term holder, more than 1.4 shares had been sold short. Closing those positions requires buying back 1.4 shares for every 1 that exists, which mathematically forces the price up.

The hedge funds doing the shorting (Melvin Capital and others) had a thesis that GameStop was a dying retailer that would eventually go to zero. The thesis wasn't crazy. The position size relative to the float was reckless. Once the buying pressure started, there was no clean way out.

The Gamma Squeeze: Options as a Force Multiplier

Layered on top of the short squeeze is a gamma squeeze. A call option is a contract that gives the holder the right to buy a stock at a specific price (the strike) within a specific time window. Market makers (Citadel, Susquehanna, Wolverine) sell those options to retail buyers and hedge their position by buying the underlying stock to cover what they'd owe if the option ends up in the money.

When a stock moves up sharply, more call options become at-the-money, and the market makers have to buy more of the underlying stock to maintain their hedge. That buying pushes the stock up further, which puts more options in the money, which forces more buying. It's a feedback loop, and it's known as a gamma squeeze because gamma is the math term for the rate at which an option's hedging requirement changes.

WallStreetBets users figured out, collectively, that GameStop was unusually exposed to a gamma squeeze. They started buying short-dated, out-of-the-money calls in volumes that were genuinely large for a stock of GameStop's market cap. The market makers had to hedge. The stock moved up. The hedging requirement increased. The cycle compounded.

The WallStreetBets Layer

The Reddit forum r/WallStreetBets is the social layer that coordinated the buying. The thesis on the forum was that GameStop was massively over-shorted, that the company's fundamentals were improving (Ryan Cohen joined the board, the stock was already up from $4 in 2020), and that retail buying could trigger the squeeze. The thesis was correct. What no one expected was the speed.

The coordination was loose. There was no central organizer. There were a few prominent posters (DeepFuckingValue, whose real name is Keith Gill, and who'd been long GameStop for over a year) whose positions and analyses got widely read. The buying decisions were millions of individual choices made by retail investors who'd read the same posts.

The institutional response (Melvin Capital taking a $2.75 billion bailout from Citadel and Point72, Robinhood restricting buying of GameStop on January 28) crystallized the narrative. What had been a financial event became a populist one. The rally accelerated.

What This Tells You About the Markets

Two structural lessons are clearly true. First, the equity market's plumbing assumes that retail traders are a passive, distributed force. When retail coordinates (through Reddit, Discord, or anything else) and concentrates on a specific over-shorted small-cap, the plumbing breaks in interesting ways. The institutional short side wasn't sized for this scenario, and the brokerage clearing infrastructure (the T+2 settlement layer) hit collateral limits that forced Robinhood and others to restrict buying.

Second, options market structure has changed. Retail call buying through commission-free brokers is a much larger fraction of total option volume than it was even three years ago. The gamma squeeze is a real, repeatable mechanic, and you should expect more of these going forward, not fewer.

What Happens Next

The short squeeze is largely over by the time you're reading this. Most of the over-short positions have been closed at large losses. The remaining buying pressure is momentum and FOMO, not structural force. The stock will probably drift down over the coming months, with regular volatility spikes as remaining shorts cover or new attempts get made.

The longer-term story is regulatory. The SEC is going to look at the short interest reporting (which lags reality by weeks), at Robinhood's order flow arrangements with Citadel, and at whether the gamma squeeze mechanic is fair to the retail buyers who don't fully understand it. None of those reviews will conclude quickly. The structural change to retail investing, if there is one, won't show up in regulation; it'll show up in how brokerages and market makers price the risk of the next coordinated squeeze.