interesting19 Nov 2017 20:18
Shorts need to control the stock's share price over a long time (often several months to well over a year), and can't afford to just accumulate an unlimited number of short positions in the stock, so they have to be buying shares at the same time they are selling shares too. When the shorts drive the share price down, eliminating buyers as discussed above, some of those investors trying to sell their shares at that same time will follow the share price activity downward lowering their ask price.
Now the shorts can buy back some of the shares they have shorted at lower prices including some shares where longs have put stop-loss sale orders to protect against downside losses. The shorts will only buy shares part of the way back up as the share price rises, and then wait to see if new buyers come into the market. If the share price continues to rise up to much again during the day, the shorts will repeat the same selling and buying process to control the share price.
As mentioned above, the shorts need to control the share price over an extended period of time. They need to wear down the longs with rumor mongering as well as by creating fear as the longs continue to see the share price go down from the computerized trading. They hope the longs will give up and sell their shares at the lowest possible share price.