I asked someone on twitter who used to be an MM about 911 trades. He currently has a podcast. This was his response.. Don't know him personally so take it with a grain of salt....
"listen to the first podcast as JJ was a market maker for 20 plus years and explains in details exactly what goes on. As for 911 signals. Those were most likely all fake, MMs are alot smarter than that. You cannot know what they do as they use high frequency trading that occurs in nano seconds"
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