Please don't attack, just a thought
Let's say a major Investment Bank or two, working as a proxy for the working committee, slowly starts buying 200 million to 500 million in futures as the market is in a steady decline. Arbs take notice of the price disparity and immediately start shorting futures while buying the underlying stocks, causing a sudden trend reversal. This also causes shorts to cover and investors to stop selling. Indices rapidly erase their losses for the day. Then the IBs, ever so carefully, begin unwinding their long futures contracts for a minor loss or gain on behalf of their client.
What's wrong with the above? And if there is no PPT, this seems like an incredibly good idea for the government to deploy in the event of a market crash.
Again, just a thought.