Step 1. Major fund decides it needs to rebalance the portfolio....

Step 1. Major fund decides it needs to rebalance the portfolio.
Step 2. Other majors or related entities get wind of the coming massive sales and start shorting.
Step 3. Morons on Hotcopper start talking rubbish about what a crap company it is (Which it may or may not be).
Step 4. Retail punters read stupid posts and without doing their own research they sell.
Step 5. Punters on Hotcopper start asking why the big drop.
Step 6. Morons ignore the rebalancing and talk more crap about the company.

Simple.