(edited) I can (and have) have set stop loss (and stops to enter a buy order) with TDA. You have to set a limit price as well as an activation price. However, I don't believe there are large or multiple stop orders sitting down at this price.
Having said all of this, its possible that there have been stop/limit orders set off which explains why for example,Friday there was a large invisible to L2 sell order @ 40 and apparently today now @ 38.
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