Quote from slidertrader:
This has nothing to do with the specialist. The specialist hardly takes part in these small orders in the new hybrid market. The vast majority of matches are done in the electronic book - just like ARCA/INET etc. If Level II is showing INET at top of book and NYSE is a nickel lower, then when your stop is triggered and it sends a market order to sell, you will take out INET and then get filled for the remaining on NYSE a nickel lower.
If NYSE was on the inside, then you would get filled there first and the better price.
If you send your stop order to NYSE, and INET is on the inside, they are required (reg NMS) to route your order to the best quote (INET).