When there is a large imbalance on the stock due to news or an index rebalance then some guys will get a position near the close in the direction of the imbalance. Then put in an offsetting MOC order hoping to close out the trade on a nice MOC print. Big examples would be AOL when added to the S&P in the late 90's for a $10 profit and GS a few years ago for $5. The good ones are few and far between these days.
What time do you have to enter in the MOC order for it to be valid? meaning doesnt it have to be entered in 20 min before the close, or can you enter a moc at any time?
What time do you have to enter in the MOC order for it to be valid? meaning doesnt it have to be entered in 20 min before the close, or can you enter a moc at any time?