Market on Close orders, MOC, must be submitted to the NYSE by 345 EST. I sometimes see a mild flurry then. But it is the MOC orders on the NASDAQ, which must be submitted by 350 EST, which just about every time create the far larger surge. If one can anticipate which direction that surge is more likely to take, profit! Otherwise might be best to step aside for a minute or two if day trading. Sometimes there is follow through, other times reversal of the initial 350 surge ...