2010-02-24 a modified version of a rule known as the UpTick rule was adopted and implemented by The U.S. Securities and Exchange Commission (SEC). It is triggered when a security’s price decreases by 10% or more from the previous day’s closing price and is effective until the close of the next day. more
The uptick rule is a trading restriction that states that short selling a stock is only allowed on an uptick. For the rule to be satisfied, the short must be either at a price above the last traded price of the security, or at the last traded price when the most recent movement between traded prices was upward (i.e. the security has traded below the last-traded price more recently than above that price). – Wikipedia
That said, Tesla Stock short-seller was implemented today because the sell-off triggered the Uptick rule.
In March 28, 2008 Jim Cramer of CNBC offered the opinion that the absence of the uptick rule harms the stock market today. He claimed that reintroducing the uptick rule would help stabilize the banking sector.
The drop of Tesla Share from $968 to $687 in a matter of minutes from Tuesday to Wednesday opening was enough to trigger this rule.
According to Teslamotorsclub: someone was short-selling in heavy volumes on
Frankfurt Xetra to keep the TSLA price down . The poster suggested that it could have been in coordination with the Nasdaq open for a bear attack.