做空指的是高价借入股票、卖掉，再以低价买入归还，从中赚取差价——如果股票没涨价的话。最近的头条都是关于所谓的主动做空者（activist shorts），虽然他们只占所有做空者的一小部分。大部分卖空行为都是对冲基金或投资机构做的，为的是对冲股价下跌风险，或者因为他们觉得股票价格虚高了。与此不同，主动做空者会对公司进行调研，寻找他们觉得有不实交易或假账的公司作为猎物，散布消息（通常是匿名的），如果一切顺利，就坐等股票下跌。虽然主动做空者几十年来一直在号召新人加入，但他们队伍的壮大得益于近几年社交媒体促进了对相关分析和理论的传播。根据Activist Insight Ltd的数据，2017年，做空机构共向全球186家公司开战，2013年是130家。战场也蔓延了，他们把目光转向了澳大利亚、日本、新加坡和南非。今年6月，港股新秀丽公司的CEO因为被空头控其学历造假而辞职。许多权威人士都不喜欢做空行为，纽交所前主席说做空“令人作呕、毫不符合美国作风”。
批评家认为做空会把市场不景气变成彻彻底底的恐慌。他们还指出做空者能在卖出前散布谣言蒙骗投资者，这种手法被称为“扭曲股价、低价做空”（short and distort）。支持做空的一方称，不能因为可能有人滥用做空就唾弃所有的空头，就像不能因为有人“哄抬股价、高价卖出”（pump and bump）就让所有因为对某只股票感兴趣而推高其股价的投资者因此蒙羞。做空者说他们只是怀疑主义者，通过找出被分析师、审计人员、投资者忽略的错误定价或欺诈行为，提醒投资者警惕市场一波接一波的狂欢。查诺斯的公司名为Kynikos，是英语单词“愤世嫉俗者”（cynic）的希腊词源。尽管做空经常被认定为不合法，但《大空头》里看空房地产市场的投资者却是正面形象。做空行为也从研究人员那里得到了一些支持：一篇论文发现空头有利于减少操纵收益报表的行为；另一篇论文显示，空头对美股中国企业股票走势的判断优于股票分析师。还有一篇论文的结论称，主动做空者说的往往是“正确事实”。（财富中文网）
If you buy low and sell high, chances are you’ll be richer and everybody will be happy. Sell low after borrowing high and you may be rich, but odds are quite a few people will be anything but pleased. That’s the short seller’s predicament, and why investors who bet that stocks will drop get threatened with everything from temporary restrictions to serious jail time, particularly during times of market turmoil. Shorts, as they’re known, say they’re keeping markets and companies honest. Critics say their practices can blur into market manipulation. Regulators are keeping a wary eye on them.
Short sellers borrow shares, sell them, buy them back at a lower price and profit from the difference — unless the stock rises. The biggest headlines these days are being made by so-called activist shorts, even though they account for only a small slice of short selling. Most shorting is done by hedge funds and institutional investors to cushion their investments against falling stock prices or to bet that shares have risen too high. Activists, on the other hand, research companies to find targets that they allege have dodgy business or accounting practices, spread the word (sometimes anonymously) and, if all goes as planned, watch the stock slump. Although activist shorts have been calling out companies for decades, their numbers have swelled thanks to the rise of social media as a platform for disseminating theories and analysis. In 2017, shorts began campaigns against 186 companies globally, versus 130 in 2013, according to Activist Insight Ltd. The campaigns have spread geographically, too, with shorts turning their attention to Australia, Japan, Singapore and South Africa. In June, the chief executive officer of Hong Kong-listed Samsonite International SA resigned after a short seller alleged he had falsified educational credentials. Many authorities dislike short selling — the former head of the New York Stock Exchange has described the practice as “icky and un-American.”
Dutch traders were shorting as long ago as the 1600s, including during the tulip bubble. Napoleon labeled short sellers of government securities “treasonous.” Short selling stocks — as opposed to, say, tulips — is particularly challenging because equity markets have a long-term track record of moving up rather than down. Still, it can be done. Jesse Livermore, known as the “King of the Bears,” made a fortune shorting railroad operator Union Pacific shortly before the 1906 San Francisco earthquake. The collapse of Enron Corp. in 2001 marked a notable scalp for shorts including Jim Chanos, who had been among the first to question its accounting. Starting in 2011, Muddy Waters’ Carson Block raised the profile of the new breed of activist shorts by taking aim at under-the-radar Chinese companies listed in North America, including the now bankrupt Sino-Forest Corp. The practice can be perilous: Block said he stopped shorting Chinese companies for a time because “tattooed gangsters” came looking for him. Short selling remains legal in most stock markets, unlike so-called naked short selling — shorting without having first borrowed the shares. When markets go bad, governments and regulators sometimes impose restrictions in an effort to help stem the slide. The U.S. targeted short selling during the Great Depression and joined the likes of the U.K., Germany and Japan in limiting short selling or banning it during the financial crisis that erupted in 2008. China’s regulator blamed “malicious” short selling in part for a stock market crash in 2015, placing limits on the practice as well as arresting traders.
Critics say short sellers can transform downturns into full-blown panics. They also point to the ability of shorts to hoodwink investors by spreading false rumors before exiting a trade, a technique known as “short and distort.” Defenders say the potential for abuse shouldn’t discredit all shorts any more than “pump and dump” schemes disgrace all investors who whip up interest in a stock to push it higher and then sell it. Short sellers say they are skeptics who alert investors to bouts of market euphoria, identifying mispricing or deception that analysts, auditors and investors overlook. The name of Chanos’s firm is Kynikos – the Greek from which the English word “cynic” was derived. Often vilified as market outlaws, investors betting against the housing market were portrayed as the good guys in the film “The Big Short.” Shorts have some backing from researchers: One paper found that the practice discourages the manipulation of earnings reports, while another showed that shorts made more accurate predictions of the share performance of U.S.-listed Chinese firms than stock analysts did. A third concluded that activist shorts were usually “factually right.”