Flash Surge in World’s Biggest ETF Linked to ‘Outlandish’ Trades

ISOs powered sudden spike in SPY on Monday.
Thin liquidity, human error are suspects in single-second jump.
On Monday, SPY spiked to $378.46, for less than one second.

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More than 150,000 trades were executed at $370 or above, totaling almost $58 million.
SPY’s spike blamed on intermarket sweep orders.
ISOs are automated trades that “sweep” the market picking up as many shares as possible at the best price available.

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When liquidity is low or ISOs are being used aggressively, it raises the possibility they can rapidly consume the better-priced shares at a single exchange and keep going -- paying more and more to fill the order.

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On Monday about 96 million shares of SPY changed hands, below the average of almost 102 million shares.
Observers to conclude the spike was more likely human error rather than a structural glitch.

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The number of transactions surged fill almost 66 screens and about 85% of them are marked as ISOs.

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