Doc nailed the process. Shorts load up on shares to dump on key days like when fins are released or other big event days so they can control the price movement of the stock and keep it contained. The shorts show up at the ask at those times with big blocks to sell and, at same time,  bidwhack the bid lower and lower until buyers throw in the towel and the price goes red. It's all about controlling the stock, as that article talks about.