Net sell orders from all 'Market on Open' and/or 'Market on Close' orders. CSCO again had a (net) Sell on Open imbalance today of 227,528 shares. Not sure what the parameters are, but, I believe the market maker reports these order imbalances before the open/close when it is expected the imbalance is large enough to have a sizable influence on the opening/closing price..... like a 'heads up' call.