The stock becomes unrestricted when a certain stipulation put on by the company is met. That is why companies issue restricted stock. Otherwise what would keep CEO's from selling and bailing? But, even so- by law there is the 6 month stipulation as well. So he can't meet a goal in 3 months and sell. He must wait 6 months at least. And then, again, he must still meet the protocol and agreement he made with the company when that stock was issued. And of course only company insiders know what that agreement is.
A number of things can cause a stock to become unrestricted. All depends on how it is set up by the company. Can be released based on holding a certain amount of time, reaching certain goals or other arrangements. He would lose his stock if he just left his company though.
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