Was it an "all or none" order? If the 10 didn't match, they couldn't place the trade.
Yes, it was an all or none. Maybe that was it.
dont use that if the size shown is already what you want
duh
OK, I didn't realize that meant that one trader had to take all 10; I thought it just meant all 10 would be taken by the another party.
In fast markets &/or low volume options the MMs will show only 1 contract @ a given price so not to get slapped with a big order they have no home for.
So for level 2 options data, if I see quantity as 1 on the OPRA BBO this truly means only one contract is being offered or is there some round lot specification (like 10 contracts = 1 unit)?
1 contract = 100 shares.
Also there are "Hidden Orders" where for instance 1 could mean in reality the MM/exchange has 250-500-XXX contracts to fill but only "shows" say 5 the remainder being "hidden" so not to spook the market!
Here you go: https://www.interactivebrokers.com/en/index.php?f=596
If you are new @ this, I'd recommend getting the bible of the options traders: "Options as a Strategic investment" by Larry McMillan! I am not sure what is the latest Edition.
G'luck