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Efficient markets hypothesis and performance of IPO shares after lock-up period
Who's to say it wasn't priced into the markets, at least to some degree? Without any information on the behaviour of holders pre-expiry, no one can know if they've been shorting the stock in advance of selling on expiry day. And with the float being such a small proportion of the total issuance, there's always the risk of sudden fluctuations picking up big momentum - which could easily explain the 7% drop on expiry day. Add into all this uncertainty, the usual risks of shorting (e.g. limited upside, unlimited downside), and the observed phenomena aren't by any means killer blows of the Efficient Market Hypothesis. That's not to say that such evidence doesn't necessarily exist - just that this isn't it.