Why would this limit order not get filled?

If the NBBO in a stock is $7.5 and $7.6, and I put a limit buy order in NSDQ route at $7.51, then 1 second later I see a sell print on the T&S at $7.5, and my bid didn't get filled at all, is there a legitimate reason for this? I thought RegNMS will ensure that print will get routed to NSDQ if my order is NBBO?

 

Was it an odd lot? <100 shares?

 

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Semi-liquid stock with a huge bid/ask; sounds like you may have to pay up;
or find something more liquid. I like stuff liquid enough for market orders/exit but I guess that is not liquid enough for a good market order...……………………………………………………………...

 

I bet it was. Not uncommon.
Or, it's a timing issue (trade was done before his order hits the book).

 

Either oddlot, the print on the tape was from a darkpool or your flow is internalized...meaning it doesn't get routed anywhere.

 

Yeah. Does this basically mean odd lots can't get filled when resting passively in the book until the NBBO literally crosses with my order?

 

It was an odd lot but I am using direct routes (no iternalization). Does this basically mean odd lots can't get filled when resting passively in the book until the NBBO literally crosses with my order?

 

That's correct. Odd lots usually get passed thru.

 

Mystery solved. Thanks.

 

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And i wonder why his broker, who makes money off bid/ ask, did not fill that buy order.
Even a medium volume semi- liquid stock can make money= must be with a wide bid ask of $7.50/7.60, NO one wants to fill a buy order of $7.51.[unless the market is dropping+ that stock has most likely dropped a lot, with NQ making news highs/new highs............................................................................................]In other words with a wide bid ask spread, not many want to work for penny/ peanuts-even though i dont blame him for asking.