KOSPI Plunges 5%, Sell-Side Circuit Breaker Triggered: 5 Reasons 'Black Tuesday' Led to the 6,000-Point Collapse

One-line hook: KOSPI, which had surged as high as 6,244, collapsed below the 5,900 mark in a single day — here are 5 diagnoses of the 'Black Tuesday' when the Iran shockwave struck Korea's stock market head-on.

TL;DR

• Following U.S.-Israeli airstrikes on Iran (beginning February 28), KOSPI plunged 5.09% intraday to 5,896.35 on March 3
• Sell-side circuit breaker triggered at 12:05 PM — the first time since January 6 of this year
• Samsung Electronics and SK Hynix each tumbled over 8%, with '200k-won Samsung' and '1M-won Hynix' thresholds also breached
• Foreign and institutional net selling combined: approximately ₩5 trillion; retail investors defended with ₩4.9 trillion in net buying
• International crude oil (Brent) at $78 per barrel, with fears of further spike on Hormuz Strait closure news

📌 Facts: What Happened

On the morning of March 3, KOSPI opened at 6,165.15, down 78.98 points (1.26%) from the previous session. Foreign investors sold a net ₩2 trillion in the morning, but strong retail buying defended the index near 6,180.

However, as the afternoon session saw foreign and institutional selling overwhelm retail buying, the decline accelerated rapidly. At 12:05 PM, the KOSPI 200 futures index recorded 890.05 — down 47.75 points (5.09%) from the prior day, triggering a sell-side circuit breaker. Program sell orders were halted for five minutes.

As of 2:07 PM, KOSPI stood at 5,896.35, falling below the 5,900 mark. More than 250 points (approximately 4.3%) evaporated in a single day.

🔥 Why It Collapsed So Fast: 5 Spreading Factors

1. Iran Airstrikes — A Longer Front Than Expected

The U.S.-Israeli airstrikes began on February 28, but Korea's market was closed through March 2 (Monday) for the Independence Movement Day holiday. The March 3 opening effectively forced the market to absorb three days' worth of bad news at once.

2. Hormuz Strait Closure News

After Iran declared a blockade of the Hormuz Strait, Brent crude surpassed $78 per barrel. With approximately one-third of the world's seaborne oil exports transiting the strait, fears of an energy supply chain collapse spread rapidly.

3. Foreign Panic Selling — A ₩5 Trillion Bomb

Foreigners dumped an unprecedented ₩4.9565 trillion in net selling in a single day — an acute manifestation of the flight from emerging-market assets sensitive to geopolitical risk.

4. Dual Vulnerability: Exports and Energy

Korea has high dependence on energy imports and significant Middle East export exposure (excluding shipbuilding and defense). A fast-forming vicious-cycle narrative emerged: oil price surge → inflation pressure → risk of resumed rate hikes.

5. Forced Liquidation of Leveraged Positions

As KOSPI had rapidly broken above 6,000, leveraged ETF and futures positions had been building. Once the sell-off began, margin calls and stop-loss orders triggered a chain reaction of forced selling.

🌐 Context and Background

KOSPI rose from 3,021 on June 20 last year to 6,083 on February 27 this year — nearly doubling in 250 trading sessions. This was a record-setting rally, the fastest doubling among major global markets. Such a steep climb can itself sow the seeds of a sharp decline, as profit-taking supply builds up thickly.

Korea Investment & Securities noted that "even if oil prices rise due to the Iran situation, the impact on the stock market will be limited," citing benefits for the shipbuilding and defense sectors. Indeed, Hanwha Aerospace surged 11% immediately after the open, underscoring a clear differentiation in defense stocks.

🔮 Outlook

✅ Checklist

📎 References

• KOSPI Falls Below 5,900, Sell-Side Circuit Breaker Triggered — Dong-A Ilbo
• KRX issues sell-side circuit breaker — Yonhap (EN)
• Korea Leads Asian Stocks Lower — Bloomberg
• Iran Strike Impact Limited, Shipbuilding & Defense to Benefit — Global Economic
• KOSPI Breaks 6,000, Fear Index Hits Record High — Yonhap

Image source: Wikimedia Commons (Seoul panoramic view)