Normally, if some orders show up one one side, locals can try to front-run them by picking off orders on the other side. If there is nobody on the opposite side to pick off, that's an air pocket.


Lean is when you use some known orders as like a backstop, and then try to gamble ahead of them. You know that if the market starts to go against you, you can dump into those orders. So if I am an NYSE specialists, and I have an order to buy 200,000 on my book at 10 1/8, I can lean on that order by bidding at 10 1/4, and trying to sell out at 10 1/2.


By lean on the cash ticker, I basically meant that if "fair" premium is 3.00, and the cash is at 1143.00, the locals will be happy to fill your market sell order in the futures at 1143.00, even if there is no hint of ambient demand in the pit. You could say they are "leaning" on cash-futures arbs, but that would be unnecessarily descriptive. Leaning just means you're not free floating, but are comparing your buy price to something, I guess.


eLROY