Legging In

See: Leg Out.

You put your good leg in...you put your bad leg out. And you do the hokey pokey as you turn yourself about.

Something like that, anyway. It was Adele or maybe Gaga who sang it.

Anyway, "legging in" refers to the process of buying a meaningful position, usually in stocks, as performed by large institutional buyers who have to worry about trading liquidity in the security they want to buy.

Like...Fidelity might decide that MSFT has finally gotten its act together, and wants to own 100 million shares. If they try to buy more than 10 million on any given day, they'll push upward the price of the stock, making the cost of gaining that position more expensive. That would be bad.

So they leg in, buying 5 million shares one day, then nothing the next, then 3 million the next. Then they stop. The brokers front-running them (i.e. buying shares ahead of them, marking up the price and then re-selling to them) might then not be "tipped off" to the notion that Fido wants 100 million shares. They then might leg in another 10 or 15 or 20 million shares on a weak market day when those shares are easier to buy. In the process of this hokey pokey, over a few weeks or so, they'll have "quietly" snarfed up the 100 million shares that they wanted for a full position in the stock, and then pray that it goes up. Or whatever they do to make gains in stocks at Fido. Woof.