They were too fast to short the stock. They could have waited for TMM to go to $4. However, they will cough up the shares they shorted when some institutional start buying.

Please read on:

Naked short selling, or naked shorting, is the practice of short-selling a tradable asset of any kind without first borrowing the security or ensuring that the security can be borrowed, as is conventionally done in a short sale. When the seller does not obtain the shares within the required time frame, the result is known as a "failure to deliver". The transaction generally remains open until the shares are acquired by the seller, or the seller's broker settles the trade.[1]

Short selling is used to anticipate a price fall, but exposes the seller to the risk of a price rise.

In 2008, the SEC banned what it called "abusive naked short selling"[2] in the United States, as well as some other jurisdictions, as a method of driving down share prices. Failing to deliver shares is legal under certain circumstances, and naked short selling is not per se illegal.[3][4][5] In the United States, naked short selling is covered by various SEC regulations which prohibit the practice.[6]

Critics, including Overstock.com's Patrick M. Byrne, have advocated for stricter regulations against naked short selling. In 2005, "Regulation SHO" was enacted, requiring that broker-dealers have grounds to believe that shares will be available for a given stock transaction, and requiring that delivery take place within a limited time period.[4][7]

As part of its response to the crisis in the North American markets in 2008, the SEC issued a temporary order restricting short-selling in the shares of 19 financial firms deemed systemically important, by reinforcing the penalties for failing to deliver the shares in time.[8] Effective September 18, 2008, amid claims that aggressive short selling had played a role in the failure of financial giant Lehman Brothers, the SEC extended and expanded the rules to remove exceptions and to cover all companies, including market makers.[2][9]

Some commentators have contended that despite regulations, naked shorting is widespread and that the SEC regulations are poorly enforced. Its critics have contended that the practice is susceptible to abuse, can be damaging to targeted companies struggling to raise capital, and has led to numerous bankruptcies.[6][10] However, other commentators have said that the naked shorting issue is a "devil theory",[11] not a bona fide market issue and a waste of regulatory resources.[