Who Sold Citi at $29.42?

Citigroup Building
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Citigroup Building

I was asked about some trading in Citigroup that occurred about 10:27am ET Monday morning.

Citi went from $29.80 to $29.42...a drop of 38 cents, or 1.3 percent. In about a second.

Now, this is not a huge percentage drop, but hey, this is Citi, one of the most liquid stocks in the world, not some below-$1 pink sheet phenomenon.

And the amount traded was a bit weird: there was a large bid in the market at $29.80 — that got hit. And then some: a series of big blocks changed hands: 594,000 shares, 79,000 shares, 71,000 shares, 47,000 shares, 37,000 shares, 17,000 shares, and at least four trades of a little more than 10,000 shares each.

That's 850,000 shares sold, in 10 trades. All in less than a second. All at $29.80.

And that's just the block trades. Altogether, there was well north of a million shares that traded near $29.80. In about a second.

But then — here's the strange part — they just kept going. Several hundred thousand additional shares traded in that same second, all the way down to $29.42.

In the parlance of Wall Street, someone swept the book.

Why would someone keep selling, even though the price was down almost 40 cents? Hard to say, but the obvious answer is someone was eager to get rid of a lot of stock. It's hard to liquidate a million shares at a time. Someone obviously wanted to get out, and when someone came by to offer to take a million shares off their hands at $29.80, and you’re dying to sell 1.5 million — and you can do it fast — you do it.

After all, how often does someone put up bids for hundreds of thousands of shares? Not very often. Trading today is dominated by an endless stream of bids and offers for 100 shares.

What does this mean? I don't really have any complaints about this from a market-structure perspective. I'm not blaming any machines (this time).

I do wonder who sold Citi at $29.43.

—By CNBC’s Bob Pisani

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